1. Allan Davis
  2. RubyLearning

Source

RubyLearning / ProjectTrak / vendor / rails / railties / doc / guides / html / getting_started_with_rails.html

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
	<title>Getting Started With Rails</title>
	<!--[if lt IE 8]>
	<script src="http://ie7-js.googlecode.com/svn/version/2.0(beta3)/IE8.js" type="text/javascript"></script>
	<![endif]-->
	<link href="stylesheets/base.css" media="screen" rel="Stylesheet" type="text/css" />
	<link href="stylesheets/forms.css" media="screen" rel="Stylesheet" type="text/css" />
	<link href="stylesheets/more.css" media="screen" rel="Stylesheet" type="text/css" />
	<style type="text/css">
		div#container {
	max-width: 900px;
	padding-bottom: 3em;
}

div#content {
	margin-left: 200px;
}

div#container.notoc {
	max-width: 600px;
}

.notoc div#content {
	margin-left: 0;
}

pre {
	line-height: 1.4em;
}

#content p tt {
	background: #eeeeee;
	border: solid 1px #cccccc;
	padding: 3px;
}

dt {
	font-weight: bold;
}

#content dt tt {
	font-size: 10pt;
}

dd {
	margin-left: 3em;
}

#content dt tt, #content pre tt {
	background: none;
	padding: 0;
	border: 0;
}

#content .olist ol {
	margin-left: 2em;
}

#header {
	position: relative;
	max-width: 840px;
	margin-left: auto;
	margin-right: auto;
}

#header.notoc {
	max-width: 580px;
}

#logo {
	position: absolute;
	left: 10px;
	top: 10px;
	width: 110px;
	height: 140px;
}

div#header h1#site_title {
	background: url('images/ruby_on_rails_by_mike_rundle2.gif') top left no-repeat;
	position: absolute;
	width: 392px;
	height: 55px;
	left: 145px;
	top: 20px;
	margin: 0;
	padding: 0;
}

#site_title span {
	display: none;
}

#site_title_tagline {
	display: none;
}

ul#navMain {
	position: absolute;
	margin: 0;
	padding: 0;
	top: 97px;
	left: 145px;
}

.left-floaty, .right-floaty {
	padding: 15px;
}

.admonitionblock,
.tableblock {
	margin-left: 1em;
	margin-right: 1em;
	margin-top: 0.25em;
	margin-bottom: 1em;
}

.admonitionblock .icon {
	padding-right: 8px;
}

.admonitionblock .content {
	border: solid 1px #ffda78;
	background: #fffebd;
	padding: 10px;
	padding-top: 8px;
	padding-bottom: 8px;
}

.admonitionblock .title {
	font-size: 140%;
	margin-bottom: 0.5em;
}

.tableblock table {
	border: solid 1px #aaaaff;
	background: #f0f0ff;
}

.tableblock th {
	background: #e0e0e0;
}

.tableblock th,
.tableblock td {
	padding: 3px;
	padding-left: 5px;
	padding-right: 5px;
}

.sidebarblock {
	margin-top: 0.25em;
	margin: 1em;
	border: solid 1px #ccccbb;
	padding: 8px;
	background: #ffffe0;
}

.sidebarblock .sidebar-title {
	font-size: 140%;
	font-weight: 600;
	margin-bottom: 0.3em;
}

.sidebarblock .sidebar-content > .para:last-child > p {
	margin-bottom: 0;
}

.sidebarblock .sidebar-title a {
	text-decoration: none;
}

.sidebarblock .sidebar-title a:hover {
	text-decoration: underline;
}

	</style>
</head>
<body>
	<div id="header" >
		<div id="logo">
			<a href="index.html" title="Ruby on Rails"><img src="images/rails_logo_remix.gif" alt="Rails" height="140" width="110" /></a>
		</div>
		
		<h1 id="site_title"><span>Ruby on Rails</span></h1>
		<h2 id="site_title_tagline">Sustainable productivity for web-application development</h2>

		<ul id="navMain">
			<li class="first-child"><a href="http://www.rubyonrails.org/" title="Ruby on Rails" class="ruby_on_rails">Ruby on Rails</a></li>
			<li><a class="manuals" href="index.html" title="Manuals Index">Guides Index</a></li>
		</ul>
	</div>

	<div id="container">
		
		<div id="sidebar">
			<h2>Chapters</h2>
			<ol>
					<li>
					<a href="#_this_guide_assumes">This Guide Assumes</a>
					</li>
					<li>
					<a href="#_what_is_rails">What is Rails?</a>
						<ul>
						
							<li><a href="#_the_mvc_architecture">The MVC Architecture</a></li>
						
							<li><a href="#_the_components_of_rails">The Components of Rails</a></li>
						
							<li><a href="#_rest">REST</a></li>
						
						</ul>
					</li>
					<li>
					<a href="#_creating_a_new_rails_project">Creating a New Rails Project</a>
						<ul>
						
							<li><a href="#_installing_rails">Installing Rails</a></li>
						
							<li><a href="#_creating_the_blog_application">Creating the Blog Application</a></li>
						
							<li><a href="#_configuring_a_database">Configuring a Database</a></li>
						
						</ul>
					</li>
					<li>
					<a href="#_hello_rails">Hello, Rails!</a>
						<ul>
						
							<li><a href="#_starting_up_the_web_server">Starting up the Web Server</a></li>
						
							<li><a href="#_setting_the_application_home_page">Setting the Application Home Page</a></li>
						
						</ul>
					</li>
					<li>
					<a href="#_getting_up_and_running_quickly_with_scaffolding">Getting Up and Running Quickly With Scaffolding</a>
					</li>
					<li>
					<a href="#_creating_a_resource">Creating a Resource</a>
						<ul>
						
							<li><a href="#_running_a_migration">Running a Migration</a></li>
						
							<li><a href="#_adding_a_link">Adding a Link</a></li>
						
							<li><a href="#_working_with_posts_in_the_browser">Working with Posts in the Browser</a></li>
						
							<li><a href="#_the_model">The Model</a></li>
						
							<li><a href="#_adding_some_validation">Adding Some Validation</a></li>
						
							<li><a href="#_using_the_console">Using the Console</a></li>
						
							<li><a href="#_listing_all_posts">Listing All Posts</a></li>
						
							<li><a href="#_customizing_the_layout">Customizing the Layout</a></li>
						
							<li><a href="#_creating_new_posts">Creating New Posts</a></li>
						
							<li><a href="#_showing_an_individual_post">Showing an Individual Post</a></li>
						
							<li><a href="#_editing_posts">Editing Posts</a></li>
						
							<li><a href="#_destroying_a_post">Destroying a Post</a></li>
						
						</ul>
					</li>
					<li>
					<a href="#_drying_up_the_code">DRYing up the Code</a>
						<ul>
						
							<li><a href="#_using_partials_to_eliminate_view_duplication">Using Partials to Eliminate View Duplication</a></li>
						
							<li><a href="#_using_filters_to_eliminate_controller_duplication">Using Filters to Eliminate Controller Duplication</a></li>
						
						</ul>
					</li>
					<li>
					<a href="#_adding_a_second_model">Adding a Second Model</a>
						<ul>
						
							<li><a href="#_generating_a_model">Generating a Model</a></li>
						
							<li><a href="#_associating_models">Associating Models</a></li>
						
							<li><a href="#_adding_a_route">Adding a Route</a></li>
						
							<li><a href="#_generating_a_controller">Generating a Controller</a></li>
						
							<li><a href="#_building_views">Building Views</a></li>
						
							<li><a href="#_hooking_comments_to_posts">Hooking Comments to Posts</a></li>
						
						</ul>
					</li>
					<li>
					<a href="#_what_s_next">What's Next?</a>
					</li>
					<li>
					<a href="#_changelog">Changelog</a>
					</li>
			</ol>
		</div>
		
		<div id="content">
				<h1>Getting Started With Rails</h1>
			<div id="preamble">
<div class="sectionbody">
<div class="para"><p>This guide covers getting up and running with Ruby on Rails.  After reading it, you should be familiar with:</p></div>
<div class="ilist"><ul>
<li>
<p>
Installing Rails, creating a new Rails application, and connecting your application to a database
</p>
</li>
<li>
<p>
The general layout of a Rails application
</p>
</li>
<li>
<p>
The basic principles of MVC (Model, View Controller) and RESTful design
</p>
</li>
<li>
<p>
How to quickly generate the starting pieces of a Rails application.
</p>
</li>
</ul></div>
</div>
</div>
<h2 id="_this_guide_assumes">1. This Guide Assumes</h2>
<div class="sectionbody">
<div class="para"><p>This guide is designed for beginners who want to get started with a Rails application from scratch. It does not assume that you have any prior experience with Rails. However, to get the most out of it, you need to have some prerequisites installed:</p></div>
<div class="ilist"><ul>
<li>
<p>
The <a href="http://www.ruby-lang.org/en/downloads/">Ruby</a> language
</p>
</li>
<li>
<p>
The <a href="http://rubyforge.org/frs/?group_id=126">RubyGems</a> packaging system
</p>
</li>
<li>
<p>
A working installation of <a href="http://www.sqlite.org/">SQLite</a> (preferred), <a href="http://www.mysql.com/">MySQL</a>, or <a href="http://www.postgresql.org/">PostgreSQL</a>
</p>
</li>
</ul></div>
<div class="para"><p>It is highly recommended that you <strong>familiarize yourself with Ruby before diving into Rails</strong>. You will find it much easier to follow what's going on with a Rails application if you understand basic Ruby syntax. Rails isn't going to magically revolutionize the way you write web applications if you have no experience with the language it uses. There are some good free resources on the net for learning Ruby, including:</p></div>
<div class="ilist"><ul>
<li>
<p>
<a href="http://www.humblelittlerubybook.com/">Mr. Neigborly’s Humble Little Ruby Book</a>
</p>
</li>
<li>
<p>
<a href="http://www.rubycentral.com/book/">Programming Ruby</a>
</p>
</li>
<li>
<p>
<a href="http://poignantguide.net/ruby/">Why's (Poignant) Guide to Ruby</a>
</p>
</li>
</ul></div>
</div>
<h2 id="_what_is_rails">2. What is Rails?</h2>
<div class="sectionbody">
<div class="para"><p>Rails is a web development framework written in the Ruby language. It is designed to make programming web applications easier by making several assumptions about what every developer needs to get started. It allows you to write less code while accomplishing more than many other languages and frameworks. Longtime Rails developers also report that it makes web application development more fun.</p></div>
<div class="para"><p>Rails is <em>opinionated software</em>. That is, it assumes that there is a best way to do things, and it's designed to encourage that best way - and in some cases discourage alternatives. If you learn "The Rails Way" you'll probably discover a tremendous increase in productivity. If you persist in bringing old habits from other languages to your Rails development, and trying to use patterns you learned elsewhere, you may have a less happy experience.</p></div>
<div class="para"><p>The Rails philosophy includes several guiding principles:</p></div>
<div class="ilist"><ul>
<li>
<p>
DRY - "Don't Repeat Yourself" - suggests that writing the same code over and over again is a bad thing.
</p>
</li>
<li>
<p>
Convention Over Configuration - means that Rails makes assumptions about what you want to do and how you're going to do it, rather than letting you tweak every little thing through endless configuration files.
</p>
</li>
<li>
<p>
REST is the best pattern for web applications - organizing your application around resources and standard HTTP verbs is the fastest way to go.
</p>
</li>
</ul></div>
<h3 id="_the_mvc_architecture">2.1. The MVC Architecture</h3>
<div class="para"><p>Rails is organized around the Model, View, Controller architecture, usually just called MVC. MVC benefits include:</p></div>
<div class="ilist"><ul>
<li>
<p>
Isolation of business logic from the user interface
</p>
</li>
<li>
<p>
Ease of keeping code DRY
</p>
</li>
<li>
<p>
Making it clear where different types of code belong for easier maintenance
</p>
</li>
</ul></div>
<h4 id="_models">2.1.1. Models</h4>
<div class="para"><p>A model represents the information (data) of the application and the rules to manipulate that data. In the case of Rails, models are primarily used for managing the rules of interaction with a corresponding database table. In most cases, one table in your database will correspond to one model in your application. The bulk of your application's business logic will be concentrated in the models.</p></div>
<h4 id="_views">2.1.2. Views</h4>
<div class="para"><p>Views represent the user interface of your application. In Rails, views are often HTML files with embedded Ruby code that performs tasks related solely to the presentation of the data. Views handle the job of providing data to the web browser or other tool that is used to make requests from your application.</p></div>
<h4 id="_controllers">2.1.3. Controllers</h4>
<div class="para"><p>Controllers provide the "glue" between models and views. In Rails, controllers are responsible for processing the incoming requests from the web browser, interrogating the models for data, and passing that data on to the views for presentation.</p></div>
<h3 id="_the_components_of_rails">2.2. The Components of Rails</h3>
<div class="para"><p>Rails provides a full stack of components for creating web applications, including:</p></div>
<div class="ilist"><ul>
<li>
<p>
Action Controller
</p>
</li>
<li>
<p>
Action View
</p>
</li>
<li>
<p>
Active Record
</p>
</li>
<li>
<p>
Action Mailer
</p>
</li>
<li>
<p>
Active Resource
</p>
</li>
<li>
<p>
Railties
</p>
</li>
<li>
<p>
Active Support
</p>
</li>
</ul></div>
<h4 id="_action_controller">2.2.1. Action Controller</h4>
<div class="para"><p>Action Controller is the component that manages the controllers in a Rails application. The Action Controller framework processes incoming requests to a Rails application, extracts parameters, and dispatches them to the intended action. Services provided by Action Controller include session management, template rendering, and redirect management.</p></div>
<h4 id="_action_view">2.2.2. Action View</h4>
<div class="para"><p>Action View manages the views of your Rails application. It can create both HTML and XML output by default. Action View manages rendering templates, including nested and partial templates, and includes built-in AJAX support.</p></div>
<h4 id="_active_record">2.2.3. Active Record</h4>
<div class="para"><p>Active Record is the base for the models in a Rails application. It provides database independence, basic CRUD functionality, advanced finding capabilities, and the ability to relate models to one another, among other services.</p></div>
<h4 id="_action_mailer">2.2.4. Action Mailer</h4>
<div class="para"><p>Action Mailer is a framework for building e-mail services. You can use Action Mailer to send emails based on flexible templates, or to receive and process incoming email.</p></div>
<h4 id="_active_resource">2.2.5. Active Resource</h4>
<div class="para"><p>Active Resource provides a framework for managing the connection between business objects an RESTful web services. It implements a way to map web-based resources to local objects with CRUD semantics.</p></div>
<h4 id="_railties">2.2.6. Railties</h4>
<div class="para"><p>Railties is the core Rails code that builds new Rails applications and glues the various frameworks together in any Rails application.</p></div>
<h4 id="_active_support">2.2.7. Active Support</h4>
<div class="para"><p>Active Support is an extensive collection of utility classes and standard Ruby library extensions that are used in the Rails, both by the core code and by your applications.</p></div>
<h3 id="_rest">2.3. REST</h3>
<div class="para"><p>The foundation of the RESTful architecture is generally considered to be Roy Fielding's doctoral thesis, <a href="http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm">Architectural Styles and the Design of Network-based Software Architectures</a>. Fortunately, you need not read this entire document to understand how REST works in Rails. REST, an acronym for Representational State Transfer, boils down to two main principles for our purposes:</p></div>
<div class="ilist"><ul>
<li>
<p>
Using resource identifiers (which, for the purposes of discussion, you can think of as URLs) to represent resources
</p>
</li>
<li>
<p>
Transferring representations of the state of that resource between system components.
</p>
</li>
</ul></div>
<div class="para"><p>For example, to a Rails application a request such as this:</p></div>
<div class="para"><p><tt>DELETE /photos/17</tt></p></div>
<div class="para"><p>would be understood to refer to a photo resource with the ID of 17, and to indicate a desired action - deleting that resource. REST is a natural style for the architecture of web applications, and Rails makes it even more natural by using conventions to shield you from some of the RESTful complexities.</p></div>
<div class="para"><p>If you’d like more details on REST as an architectural style, these resources are more approachable than Fielding’s thesis:</p></div>
<div class="ilist"><ul>
<li>
<p>
<a href="http://www.infoq.com/articles/rest-introduction">A Brief Introduction to REST</a> by Stefan Tilkov
</p>
</li>
<li>
<p>
<a href="http://bitworking.org/news/373/An-Introduction-to-REST">An Introduction to REST</a> (video tutorial) by Joe Gregorio
</p>
</li>
<li>
<p>
<a href="http://en.wikipedia.org/wiki/Representational_State_Transfer">Representational State Transfer</a> article in Wikipedia
</p>
</li>
</ul></div>
</div>
<h2 id="_creating_a_new_rails_project">3. Creating a New Rails Project</h2>
<div class="sectionbody">
<div class="para"><p>If you follow this guide, you'll create a Rails project called <tt>blog</tt>, a (very) simple weblog. Before you can start building the application, you need to make sure that you have Rails itself installed.</p></div>
<h3 id="_installing_rails">3.1. Installing Rails</h3>
<div class="para"><p>In most cases, the easiest way to install Rails is to take advantage of RubyGems:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ gem install rails
</tt></pre></div></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/note.png" alt="Note" />
</td>
<td class="content">There are some special circumstances in which you might want to use an alternate installation strategy:</td>
</tr></table>
</div>
<div class="ilist"><ul>
<li>
<p>
If you're working on Windows, you may find it easier to install <a href="http://instantrails.rubyforge.org/wiki/wiki.pl">Instant Rails</a>. Be aware, though, that Instant Rails releases tend to lag seriously behind the actual Rails version. Also, you will find that Rails development on Windows is overall less pleasant than on other operating systems. If at all possible, we suggest that you install a Linux virtual machine and use that for Rails development, instead of using Windows.
</p>
</li>
<li>
<p>
If you want to keep up with cutting-edge changes to Rails, you'll want to clone the <a href="http://github.com/rails/rails/tree/master">Rails source code</a> from github. This is not recommended as an option for beginners, though.
</p>
</li>
</ul></div>
<h3 id="_creating_the_blog_application">3.2. Creating the Blog Application</h3>
<div class="para"><p>Open a terminal, navigate to a folder where you have rights to create files, and type:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ rails blog
</tt></pre></div></div>
<div class="para"><p>This will create a Rails application that uses a SQLite database for data storage. If you prefer to use MySQL, run this command instead:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ rails blog -d mysql
</tt></pre></div></div>
<div class="para"><p>And if you're using PostgreSQL for data storage, run this command:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ rails blog -d postgresql
</tt></pre></div></div>
<div class="para"><p>In any case, Rails will create a folder in your working directory called <tt>blog</tt>. Open up that folder and explore its contents. Most of the work in this tutorial will happen in the <tt>app/</tt> folder, but here's a basic rundown on the function of each folder that Rails creates in a new application by default:</p></div>
<div class="tableblock">
<table rules="all"
frame="hsides"
cellspacing="0" cellpadding="4">
<col width="137" />
<col width="1440" />
<thead>
  <tr>
    <th align="left">
    File/Folder
    </th>
    <th align="left">
    Purpose
    </th>
  </tr>
</thead>
<tbody valign="top">
  <tr>
    <td align="left">
    <tt>README</tt>
    </td>
    <td align="left">
    This is a brief instruction manual for your application. Use it to tell others what your application does, how to set it up, and so on.
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>Rakefile</tt>
    </td>
    <td align="left">
    This file contains batch jobs that can be run from the terminal.
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>app/</tt>
    </td>
    <td align="left">
    Contains the controllers, models, and views for your application. You'll focus on this folder for the remainder of this guide.
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>config/</tt>
    </td>
    <td align="left">
    Configure your application's runtime rules, routes, database, and more.
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>db/</tt>
    </td>
    <td align="left">
    Shows your current database schema, as well as the database migrations. You'll learn about migrations shortly.
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>doc/</tt>
    </td>
    <td align="left">
    In-depth documentation for your application.
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>lib/</tt>
    </td>
    <td align="left">
    Extended modules for your application (not covered in this guide).
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>log/</tt>
    </td>
    <td align="left">
    Application log files.
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>public/</tt>
    </td>
    <td align="left">
    The only folder seen to the world as-is.  This is where your images, javascript, stylesheets (CSS), and other static files go.
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>script/</tt>
    </td>
    <td align="left">
    Scripts provided by Rails to do recurring tasks, such as benchmarking, plugin installation, and starting the console or the web server.
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>test/</tt>
    </td>
    <td align="left">
    Unit tests, fixtures, and other test apparatus. These are covered in <a href="../testing_rails_applications.html">Testing Rails Applications</a>
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>tmp/</tt>
    </td>
    <td align="left">
    Temporary files
    </td>
  </tr>
  <tr>
    <td align="left">
    <tt>vendor/</tt>
    </td>
    <td align="left">
    A place for third-party code. In a typical Rails application, this includes Ruby Gems, the Rails source code (if you install it into your project) and plugins containing additional prepackaged functionality.
    </td>
  </tr>
</tbody>
</table>
</div>
<h3 id="_configuring_a_database">3.3. Configuring a Database</h3>
<div class="para"><p>Just about every Rails application will interact with a database. The database to use is specified in a configuration file, <tt>config/database.yml</tt>.
If you open this file in a new Rails application, you'll see a default database configuration using SQLite. The file contains sections for three different environments in which Rails can run by default:</p></div>
<div class="ilist"><ul>
<li>
<p>
The <tt>development</tt> environment is used on your development computer as you interact manually with the application
</p>
</li>
<li>
<p>
The <tt>test</tt> environment is used to run automated tests
</p>
</li>
<li>
<p>
The <tt>production</tt> environment is used when you deploy your application for the world to use.
</p>
</li>
</ul></div>
<h4 id="_configuring_a_sqlite_database">3.3.1. Configuring a SQLite Database</h4>
<div class="para"><p>Rails comes with built-in support for <a href="http://www.sqlite.org/">SQLite</a>, which is a lightweight serverless database application. While a busy production environment may overload SQLite, it works well for development and testing. Rails defaults to using a SQLite database when creating a new project, but you can always change it later.</p></div>
<div class="para"><p>Here's the section of the default configuration file with connection information for the development environment:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>development<span style="color: #990000">:</span>
  adapter<span style="color: #990000">:</span> sqlite3
  database<span style="color: #990000">:</span> db<span style="color: #990000">/</span>development<span style="color: #990000">.</span>sqlite3
  timeout<span style="color: #990000">:</span> <span style="color: #993399">5000</span>
</tt></pre></div></div>
<div class="para"><p>If you don't have any database set up, SQLite is the easiest to get installed. If you're on OS X 10.5 or greater on a Mac, you already have it. Otherwise, you can install it using RubyGems:</p></div>
<div class="para"><p>If you're not running OS X 10.5 or greater, you'll need to install the SQLite gem.  Similar to installing Rails you just need to run:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ gem install sqlite3-ruby
</tt></pre></div></div>
<h4 id="_configuring_a_mysql_database">3.3.2. Configuring a MySQL Database</h4>
<div class="para"><p>If you choose to use MySQL, your <tt>config/database.yml</tt> will look a little different. Here's the development section:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>development<span style="color: #990000">:</span>
  adapter<span style="color: #990000">:</span> mysql
  encoding<span style="color: #990000">:</span> utf8
  database<span style="color: #990000">:</span> blog_development
  username<span style="color: #990000">:</span> root
  password<span style="color: #990000">:</span>
  socket<span style="color: #990000">:</span> <span style="color: #FF6600">/tmp/</span>mysql<span style="color: #990000">.</span>sock
</tt></pre></div></div>
<div class="para"><p>If your development computer's MySQL installation includes a root user with an empty password, this configuration should work for you. Otherwise, change the username and password in the <tt>development</tt> section as appropriate.</p></div>
<h4 id="_configuring_a_postgresql_database">3.3.3. Configuring a PostgreSQL Database</h4>
<div class="para"><p>If you choose to use PostgreSQL, your <tt>config/database.yml</tt> will be customized to use PostgreSQL databases:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>development<span style="color: #990000">:</span>
  adapter<span style="color: #990000">:</span> postgresql
  encoding<span style="color: #990000">:</span> unicode
  database<span style="color: #990000">:</span> blog_development
  username<span style="color: #990000">:</span> blog
  password<span style="color: #990000">:</span>
</tt></pre></div></div>
<div class="para"><p>Change the username and password in the <tt>development</tt> section as appropriate.</p></div>
</div>
<h2 id="_hello_rails">4. Hello, Rails!</h2>
<div class="sectionbody">
<div class="para"><p>One of the traditional places to start with a new language is by getting some text up on screen quickly. To do that in Rails, you need to create at minimum a controller and a view. Fortunately, you can do that in a single command. Enter this command in your terminal:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ script/generate controller home index
</tt></pre></div></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">If you're on Windows, or your Ruby is set up in some non-standard fashion, you may need to explicitly pass Rails <tt>script</tt> commands to Ruby: <tt>ruby script/generate controller home index</tt>.</td>
</tr></table>
</div>
<div class="para"><p>Rails will create several files for you, including <tt>app/views/home/index.html.erb</tt>. This is the template that will be used to display the results of the <tt>index</tt> action (method) in the <tt>home</tt> controller. Open this file in your text editor and edit it to contain a single line of code:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">&lt;h1&gt;</span></span>Hello, Rails!<span style="font-weight: bold"><span style="color: #0000FF">&lt;/h1&gt;</span></span>
</tt></pre></div></div>
<h3 id="_starting_up_the_web_server">4.1. Starting up the Web Server</h3>
<div class="para"><p>You actually have a functional Rails application already - after running only two commands! To see it, you need to start a web server on your development machine. You can do this by running another command:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ script/server
</tt></pre></div></div>
<div class="para"><p>This will fire up the lightweight Webrick web server by default. To see your application in action, open a browser window and navigate to <tt>http://localhost:3000</tt>. You should see Rails' default information page:</p></div>
<div class="para"><p><span class="image">
<img src="images/rails_welcome.png" alt="Welcome Aboard screenshot" title="Welcome Aboard screenshot" />
</span></p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">To stop the web server, hit Ctrl+C in the terminal window where it's running. In development mode, Rails does not generally require you to stop the server; changes you make in files will be automatically picked up by the server.</td>
</tr></table>
</div>
<div class="para"><p>The "Welcome Aboard" page is the smoke test for a new Rails application: it makes sure that you have your software configured correctly enough to serve a page. To view the page you just created, navigate to <tt>http://localhost:3000/home/index</tt>.</p></div>
<h3 id="_setting_the_application_home_page">4.2. Setting the Application Home Page</h3>
<div class="para"><p>You'd probably like to replace the "Welcome Aboard" page with your own application's home page. The first step to doing this is to delete the default page from your application:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ rm public/index<span style="color: #990000">.</span>html
</tt></pre></div></div>
<div class="para"><p>Now, you have to tell Rails where your actual home page is located. Open the file <tt>config/routes.rb</tt> in your editor. This is your application's, <em>routing file</em>, which holds entries in a special DSL (domain-specific language) that tells Rails how to connect incoming requests to controllers and actions. At the bottom of the file you'll see the <em>default routes</em>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>map<span style="color: #990000">.</span>connect <span style="color: #FF0000">':controller/:action/:id'</span>
map<span style="color: #990000">.</span>connect <span style="color: #FF0000">':controller/:action/:id.:format'</span>
</tt></pre></div></div>
<div class="para"><p>The default routes handle simple requests such as <tt>/home/index</tt>: Rails translates that into a call to the <tt>index</tt> action in the <tt>home</tt> controller. As another example, <tt>/posts/edit/1</tt> would run the <tt>edit</tt> action in the <tt>posts</tt> controller with an <tt>id</tt> of 1.</p></div>
<div class="para"><p>To hook up your home page, you need to add another line to the routing file, above the default routes:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>map<span style="color: #990000">.</span>root <span style="color: #990000">:</span>controller <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"home"</span>
</tt></pre></div></div>
<div class="para"><p>This line illustrates one tiny bit of the "convention over configuration" approach: if you don't specify an action, Rails assumes the <tt>index</tt> action.</p></div>
<div class="para"><p>Now if you navigate to <tt>http://localhost:3000</tt> in your browser, you'll see the <tt>home/index</tt> view.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/note.png" alt="Note" />
</td>
<td class="content">For more information about routing, refer to <a href="../routing_outside_in.html">Rails Routing from the Outside In</a>.</td>
</tr></table>
</div>
</div>
<h2 id="_getting_up_and_running_quickly_with_scaffolding">5. Getting Up and Running Quickly With Scaffolding</h2>
<div class="sectionbody">
<div class="para"><p>Rails <em>scaffolding</em> is a quick way to generate some of the major pieces of an application. If you want to create the models, views, and controllers for a new resource in a single operation, scaffolding is the tool for the job.</p></div>
</div>
<h2 id="_creating_a_resource">6. Creating a Resource</h2>
<div class="sectionbody">
<div class="para"><p>In the case of the blog application, you can start by generating a scaffolded Post resource: this will represent a single blog posting. To do this, enter this command in your terminal:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ script/generate scaffold Post name<span style="color: #990000">:</span>string title<span style="color: #990000">:</span>string content<span style="color: #990000">:</span>text
</tt></pre></div></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/note.png" alt="Note" />
</td>
<td class="content">While scaffolding will get you up and running quickly, the "one size fits all" code that it generates is unlikely to be a perfect fit for your application. In most cases, you'll need to customize the generated code. Many experienced Rails developers avoid scaffolding entirely, preferring to write all or most of their source code from scratch.</td>
</tr></table>
</div>
<div class="para"><p>The scaffold generator will build 13 files in your application, along with some folders, and edit one more. Here's a quick overview of what it creates:</p></div>
<div class="tableblock">
<table rules="all"
frame="hsides"
cellspacing="0" cellpadding="4">
<col width="525" />
<col width="1062" />
<thead>
  <tr>
    <th align="left">
    File
    </th>
    <th align="left">
    Purpose
    </th>
  </tr>
</thead>
<tbody valign="top">
  <tr>
    <td align="left">
    app/models/post.rb
    </td>
    <td align="left">
    The Post model
    </td>
  </tr>
  <tr>
    <td align="left">
    db/migrate/20081013124235_create_posts.rb
    </td>
    <td align="left">
    Migration to create the posts table in your database (your name will include a different timestamp)
    </td>
  </tr>
  <tr>
    <td align="left">
    app/views/posts/index.html.erb
    </td>
    <td align="left">
    A view to display an index of all posts
    </td>
  </tr>
  <tr>
    <td align="left">
    app/views/posts/show.html.erb
    </td>
    <td align="left">
    A view to display a single post
    </td>
  </tr>
  <tr>
    <td align="left">
    app/views/posts/new.html.erb
    </td>
    <td align="left">
    A view to create a new post
    </td>
  </tr>
  <tr>
    <td align="left">
    app/views/posts/edit.html.erb
    </td>
    <td align="left">
    A view to edit an existing post
    </td>
  </tr>
  <tr>
    <td align="left">
    app/views/layouts/posts.html.erb
    </td>
    <td align="left">
    A view to control the overall look and feel of the other posts views
    </td>
  </tr>
  <tr>
    <td align="left">
    public/stylesheets/scaffold.css
    </td>
    <td align="left">
    Cascading style sheet to make the scaffolded views look better
    </td>
  </tr>
  <tr>
    <td align="left">
    app/controllers/posts_controller.rb
    </td>
    <td align="left">
    The Posts controller
    </td>
  </tr>
  <tr>
    <td align="left">
    test/functional/posts_controller_test.rb
    </td>
    <td align="left">
    Functional testing harness for the posts controller
    </td>
  </tr>
  <tr>
    <td align="left">
    app/helpers/posts_helper.rb
    </td>
    <td align="left">
    Helper functions to be used from the posts views
    </td>
  </tr>
  <tr>
    <td align="left">
    config/routes.rb
    </td>
    <td align="left">
    Edited to include routing information for posts
    </td>
  </tr>
  <tr>
    <td align="left">
    test/fixtures/posts.yml
    </td>
    <td align="left">
    Dummy posts for use in testing
    </td>
  </tr>
  <tr>
    <td align="left">
    test/unit/post_test.rb
    </td>
    <td align="left">
    Unit testing harness for the posts model
    </td>
  </tr>
</tbody>
</table>
</div>
<h3 id="_running_a_migration">6.1. Running a Migration</h3>
<div class="para"><p>One of the products of the <tt>script/generate scaffold</tt> command is a <em>database migration</em>. Migrations are Ruby classes that are designed to make it simple to create and modify database tables. Rails uses rake commands to run migrations, and it's possible to undo a migration after it's been applied to your database. Migration filenames include a timestamp to ensure that they're processed in the order that they were created.</p></div>
<div class="para"><p>If you look in the <tt>db/migrate/20081013124235_create_posts.rb</tt> file (remember, yours will have a slightly different name), here's what you'll find:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> CreatePosts <span style="color: #990000">&lt;</span> ActiveRecord<span style="color: #990000">::</span>Migration
  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> <span style="font-weight: bold"><span style="color: #0000FF">self</span></span><span style="color: #990000">.</span>up
    create_table <span style="color: #990000">:</span>posts <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>t<span style="color: #990000">|</span>
      t<span style="color: #990000">.</span>string <span style="color: #990000">:</span>name
      t<span style="color: #990000">.</span>string <span style="color: #990000">:</span>title
      t<span style="color: #990000">.</span>text <span style="color: #990000">:</span>content

      t<span style="color: #990000">.</span>timestamps
    <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> <span style="font-weight: bold"><span style="color: #0000FF">self</span></span><span style="color: #990000">.</span>down
    drop_table <span style="color: #990000">:</span>posts
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>If you were to translate that into words, it says something like: when this migration is run, create a table named <tt>posts</tt> with two string columns (<tt>name</tt> and <tt>title</tt>) and a text column (<tt>content</tt>), and generate timestamp fields to track record creation and updating. You can learn the detailed syntax for migrations in the <a href="../migrations.html">Rails Database Migrations</a> guide.</p></div>
<div class="para"><p>At this point, you need to do two things: create the database and run the migration. You can use rake commands at the terminal for both of those tasks:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ rake db<span style="color: #990000">:</span>create
$ rake db<span style="color: #990000">:</span>migrate
</tt></pre></div></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/note.png" alt="Note" />
</td>
<td class="content">Because you're working in the development environment by default, both of these commands will apply to the database defined in the <tt>development</tt> section of your <tt>config/database.yml</tt> file.</td>
</tr></table>
</div>
<h3 id="_adding_a_link">6.2. Adding a Link</h3>
<div class="para"><p>To hook the posts up to the home page you've already created, you can add a link to the home page. Open <tt>/app/views/home/index.html.erb</tt> and modify it as follows:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>Hello<span style="color: #990000">,</span> Rails!<span style="color: #FF0000">&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;%= link_to "My Blog", posts_path %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>The <tt>link_to</tt> method is one of Rails' built-in view helpers. It creates a hyperlink based on text to display and where to go - in this case, to the path for posts.</p></div>
<h3 id="_working_with_posts_in_the_browser">6.3. Working with Posts in the Browser</h3>
<div class="para"><p>Now you're ready to start working with posts. To do that, navigate to <tt>http://localhost:3000</tt> and then click the "My Blog" link:</p></div>
<div class="para"><p><span class="image">
<img src="images/posts_index.png" alt="Posts Index screenshot" title="Posts Index screenshot" />
</span></p></div>
<div class="para"><p>This is the result of Rails rendering the <tt>index</tt> view of your posts. There aren't currently any posts in the database, but if you click the <tt>New Post</tt> link you can create one. After that, you'll find that you can edit posts, look at their details, or destroy them. All of the logic and HTML to handle this was built by the single <tt>script/generate scaffold</tt> command.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">In development mode (which is what you're working in by default), Rails reloads your application with every browser request, so there's no need to stop and restart the web server.</td>
</tr></table>
</div>
<div class="para"><p>Congratulations, you're riding the rails! Now it's time to see how it all works.</p></div>
<h3 id="_the_model">6.4. The Model</h3>
<div class="para"><p>The model file, <tt>app/models/post.rb</tt> is about as simple as it can get:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> Post <span style="color: #990000">&lt;</span> ActiveRecord<span style="color: #990000">::</span>Base
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>There isn't much to this file - but note that the <tt>Post</tt> class inherits from <tt>ActiveRecord::Base</tt>. Active Record supplies a great deal of functionality to your Rails models for free, including basic database CRUD (Create, Read, Update, Destroy) operations, data validation, as well as sophisticated search support and the ability to relate multiple models to one another.</p></div>
<h3 id="_adding_some_validation">6.5. Adding Some Validation</h3>
<div class="para"><p>Rails includes methods to help you validate the data that you send to models. Open the <tt>app/models/post.rb</tt> file and edit it:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> Post <span style="color: #990000">&lt;</span> ActiveRecord<span style="color: #990000">::</span>Base
  validates_presence_of <span style="color: #990000">:</span>name<span style="color: #990000">,</span> <span style="color: #990000">:</span>title
  validates_length_of <span style="color: #990000">:</span>title<span style="color: #990000">,</span> <span style="color: #990000">:</span>minimum <span style="color: #990000">=&gt;</span> <span style="color: #993399">5</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>These changes will ensure that all posts have a name and a title, and that the title is at least five characters long. Rails can validate a variety of conditions in a model, including the presence or uniqueness of columns, their format, and the existence of associated objects.</p></div>
<h3 id="_using_the_console">6.6. Using the Console</h3>
<div class="para"><p>To see your validations in action, you can use the console. The console is a command-line tool that lets you execute Ruby code in the context of your application:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ script/console
</tt></pre></div></div>
<div class="para"><p>After the console loads, you can use it to work with your application's models:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #990000">&gt;&gt;</span> p <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>create<span style="color: #990000">(:</span>content <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"A new post"</span><span style="color: #990000">)</span>
<span style="color: #990000">=&gt;</span> <span style="font-style: italic"><span style="color: #9A1900">#&lt;Post id: nil, name: nil, title: nil, content: "A new post",</span></span>
created_at<span style="color: #990000">:</span> nil<span style="color: #990000">,</span> updated_at<span style="color: #990000">:</span> nil<span style="color: #990000">&gt;</span>
<span style="color: #990000">&gt;&gt;</span> p<span style="color: #990000">.</span>save
<span style="color: #990000">=&gt;</span> <span style="font-weight: bold"><span style="color: #0000FF">false</span></span>
<span style="color: #990000">&gt;&gt;</span> p<span style="color: #990000">.</span>errors
<span style="color: #990000">=&gt;</span> <span style="font-style: italic"><span style="color: #9A1900">#&lt;ActiveRecord::Errors:0x23bcf0c @base=#&lt;Post id: nil, name: nil,</span></span>
title<span style="color: #990000">:</span> nil<span style="color: #990000">,</span> content<span style="color: #990000">:</span> <span style="color: #FF0000">"A new post"</span><span style="color: #990000">,</span> created_at<span style="color: #990000">:</span> nil<span style="color: #990000">,</span> updated_at<span style="color: #990000">:</span> nil<span style="color: #990000">&gt;,</span>
@<span style="color: #009900">errors</span><span style="color: #990000">=</span>{<span style="color: #FF0000">"name"</span><span style="color: #990000">=&gt;[</span><span style="color: #FF0000">"can't be blank"</span><span style="color: #990000">],</span> <span style="color: #FF0000">"title"</span><span style="color: #990000">=&gt;[</span><span style="color: #FF0000">"can't be blank"</span><span style="color: #990000">,</span>
<span style="color: #FF0000">"is too short (minimum is 5 characters)"</span><span style="color: #990000">]</span>}<span style="color: #990000">&gt;</span>
</tt></pre></div></div>
<div class="para"><p>This code shows creating a new <tt>Post</tt> instance, attempting to save it and getting <tt>false</tt> for a return value (indicating that the save failed), and inspecting the <tt>errors</tt> of the post.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">Unlike the development web server, the console does not automatically load your code afresh for each line. If you make changes, type <tt>reload!</tt> at the console prompt to load them.</td>
</tr></table>
</div>
<h3 id="_listing_all_posts">6.7. Listing All Posts</h3>
<div class="para"><p>The easiest place to start looking at functionality is with the code that lists all posts. Open the file <tt>app/controllers/posts_controller.rb </tt> and look at the <tt>index</tt> action:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">def</span></span> index
  <span style="color: #009900">@posts</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(:</span>all<span style="color: #990000">)</span>

  respond_to <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>format<span style="color: #990000">|</span>
    format<span style="color: #990000">.</span>html <span style="font-style: italic"><span style="color: #9A1900"># index.html.erb</span></span>
    format<span style="color: #990000">.</span>xml  <span style="color: #FF0000">{</span> render <span style="color: #990000">:</span>xml <span style="color: #990000">=&gt;</span> <span style="color: #009900">@posts</span> <span style="color: #FF0000">}</span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>This code sets the <tt>@posts</tt> instance variable to an array of all posts in the database. <tt>Post.find(:all)</tt> or <tt>Post.all</tt> calls the <tt>Post</tt> model to return all of the posts that are currently in the database, with no limiting conditions.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">For more information on finding records with Active Record, see <a href="../finders.html">Active Record Finders</a>.</td>
</tr></table>
</div>
<div class="para"><p>The <tt>respond_to</tt> block handles both HTML and XML calls to this action. If you browse to <tt>http://localhost:3000/posts.xml</tt>, you'll see all of the posts in XML format. The HTML format looks for a view in <tt>app/views/posts/</tt> with a name that corresponds to the action name. Rails makes all of the instance variables from the action available to the view. Here's <tt>app/view/posts/index.html.erb</tt>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>Listing posts<span style="color: #FF0000">&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;table&gt;</span>
  <span style="color: #FF0000">&lt;tr&gt;</span>
    <span style="color: #FF0000">&lt;th&gt;</span>Name<span style="color: #FF0000">&lt;/th&gt;</span>
    <span style="color: #FF0000">&lt;th&gt;</span>Title<span style="color: #FF0000">&lt;/th&gt;</span>
    <span style="color: #FF0000">&lt;th&gt;</span>Content<span style="color: #FF0000">&lt;/th&gt;</span>
  <span style="color: #FF0000">&lt;/tr&gt;</span>

<span style="color: #FF0000">&lt;% for post in @posts %&gt;</span>
  <span style="color: #FF0000">&lt;tr&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%=h post.name %&gt;&lt;/td&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%=h post.title %&gt;&lt;/td&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%=h post.content %&gt;&lt;/td&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%= link_to 'Show', post %&gt;&lt;/td&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%= link_to 'Edit', edit_post_path(post) %&gt;&lt;/td&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%= link_to 'Destroy', post, :confirm =&gt;</span> <span style="color: #FF0000">'Are you sure?'</span><span style="color: #990000">,</span> <span style="color: #990000">:</span>method <span style="color: #990000">=&gt;</span> <span style="color: #990000">:</span>delete <span style="color: #990000">%&gt;</span><span style="color: #FF0000">&lt;/td&gt;</span>
  <span style="color: #FF0000">&lt;/tr&gt;</span>
<span style="color: #FF0000">&lt;% end %&gt;</span>
<span style="color: #FF0000">&lt;/table&gt;</span>

<span style="color: #FF0000">&lt;br /&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'New post', new_post_path %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>This view iterates over the contents of the <tt>@posts</tt> array to display content and links. A few things to note in the view:</p></div>
<div class="ilist"><ul>
<li>
<p>
<tt>h</tt> is a Rails helper method to sanitize displayed data, preventing cross-site scripting attacks
</p>
</li>
<li>
<p>
<tt>link_to</tt> builds a hyperlink to a particular destination
</p>
</li>
<li>
<p>
<tt>edit_post_path</tt> is a helper that Rails provides as part of RESTful routing. You’ll see a variety of these helpers for the different actions that the controller includes.
</p>
</li>
</ul></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">For more details on the rendering process, see <a href="../layouts_and_rendering.html">Layouts and Rendering in Rails</a>.</td>
</tr></table>
</div>
<h3 id="_customizing_the_layout">6.8. Customizing the Layout</h3>
<div class="para"><p>The view is only part of the story of how HTML is displayed in your web browser. Rails also has the concept of <tt>layouts</tt>, which are containers for views. When Rails renders a view to the browser, it does so by putting the view's HTML into a layout's HTML. The <tt>script/generate scaffold</tt> command automatically created a default layout, <tt>app/views/layouts/posts.html.erb</tt>, for the posts. Open this layout in your editor and modify the <tt>body</tt> tag:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #990000">&lt;!</span>DOCTYPE html PUBLIC <span style="color: #FF0000">"-//W3C//DTD XHTML 1.0 Transitional//EN"</span>
       <span style="color: #FF0000">"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"</span><span style="color: #990000">&gt;</span>

<span style="color: #FF0000">&lt;html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"&gt;</span>
<span style="color: #FF0000">&lt;head&gt;</span>
  <span style="color: #FF0000">&lt;meta http-equiv="content-type" content="text/html;charset=UTF-8" /&gt;</span>
  <span style="color: #FF0000">&lt;title&gt;</span>Posts<span style="color: #990000">:</span> <span style="color: #FF0000">&lt;%= controller.action_name %&gt;&lt;/title&gt;</span>
  <span style="color: #FF0000">&lt;%= stylesheet_link_tag 'scaffold' %&gt;</span>
<span style="color: #FF0000">&lt;/head&gt;</span>
<span style="color: #FF0000">&lt;body style="background: #EEEEEE;"&gt;</span>

<span style="color: #FF0000">&lt;p style="color: green"&gt;&lt;%= flash[:notice] %&gt;&lt;/p&gt;</span>

<span style="color: #FF0000">&lt;%= yield  %&gt;</span>

<span style="color: #FF0000">&lt;/body&gt;</span>
<span style="color: #FF0000">&lt;/html&gt;</span>
</tt></pre></div></div>
<div class="para"><p>Now when you refresh the <tt>/posts</tt> page, you'll see a gray background to the page. This same gray background will be used throughout all the views for posts.</p></div>
<h3 id="_creating_new_posts">6.9. Creating New Posts</h3>
<div class="para"><p>Creating a new post involves two actions. The first is the <tt>new</tt> action, which instantiates an empty <tt>Post</tt> object:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">def</span></span> new
  <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>new

  respond_to <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>format<span style="color: #990000">|</span>
    format<span style="color: #990000">.</span>html <span style="font-style: italic"><span style="color: #9A1900"># new.html.erb</span></span>
    format<span style="color: #990000">.</span>xml  <span style="color: #FF0000">{</span> render <span style="color: #990000">:</span>xml <span style="color: #990000">=&gt;</span> <span style="color: #009900">@post</span> <span style="color: #FF0000">}</span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>The <tt>new.html.erb</tt> view displays this empty Post to the user:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>New post<span style="color: #FF0000">&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;% form_for(@post) do |f| %&gt;</span>
  <span style="color: #FF0000">&lt;%= f.error_messages %&gt;</span>

  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :name %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_field :name %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :title %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_field :title %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :content %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_area :content %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.submit "Create" %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
<span style="color: #FF0000">&lt;% end %&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'Back', posts_path %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>The <tt>form_for</tt> block is used to create an HTML form. Within this block, you have access to methods to build various controls on the form. For example, <tt>f.text_field :name</tt> tells Rails to create a text input on the form, and to hook it up to the <tt>name</tt> attribute of the instance being displayed. You can only use these methods with attributes of the model that the form is based on (in this case <tt>name</tt>, <tt>title</tt>, and <tt>content</tt>). Rails uses <tt>form_for</tt> in preference to having your write raw HTML because the code is more succinct, and because it explicitly ties the form to a particular model instance.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">If you need to create an HTML form that displays arbitrary fields, not tied to a model, you should use the <tt>form_tag</tt> method, which provides shortcuts for building forms that are not necessarily tied to a model instance.</td>
</tr></table>
</div>
<div class="para"><p>When the user clicks the <tt>Create</tt> button on this form, the browser will send information back to the <tt>create</tt> method of the controller (Rails knows to call the <tt>create</tt> method because the form is sent with an HTTP POST request; that's one of the conventions that I mentioned earlier):</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">def</span></span> create
  <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>new<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>post<span style="color: #990000">])</span>

  respond_to <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>format<span style="color: #990000">|</span>
    <span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #009900">@post</span><span style="color: #990000">.</span>save
      flash<span style="color: #990000">[:</span>notice<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">'Post was successfully created.'</span>
      format<span style="color: #990000">.</span>html <span style="color: #FF0000">{</span> redirect_to<span style="color: #990000">(</span><span style="color: #009900">@post</span><span style="color: #990000">)</span> <span style="color: #FF0000">}</span>
      format<span style="color: #990000">.</span>xml  <span style="color: #FF0000">{</span> render <span style="color: #990000">:</span>xml <span style="color: #990000">=&gt;</span> <span style="color: #009900">@post</span><span style="color: #990000">,</span> <span style="color: #990000">:</span>status <span style="color: #990000">=&gt;</span> <span style="color: #990000">:</span>created<span style="color: #990000">,</span> <span style="color: #990000">:</span>location <span style="color: #990000">=&gt;</span> <span style="color: #009900">@post</span> <span style="color: #FF0000">}</span>
    <span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
      format<span style="color: #990000">.</span>html <span style="color: #FF0000">{</span> render <span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"new"</span> <span style="color: #FF0000">}</span>
      format<span style="color: #990000">.</span>xml  <span style="color: #FF0000">{</span> render <span style="color: #990000">:</span>xml <span style="color: #990000">=&gt;</span> <span style="color: #009900">@post</span><span style="color: #990000">.</span>errors<span style="color: #990000">,</span> <span style="color: #990000">:</span>status <span style="color: #990000">=&gt;</span> <span style="color: #990000">:</span>unprocessable_entity <span style="color: #FF0000">}</span>
    <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>The <tt>create</tt> action instantiates a new Post object from the data supplied by the user on the form, which Rails makes available in the <tt>params</tt> hash. After saving the new post, it uses <tt>flash[:notice]</tt> to create an informational message for the user, and redirects to the show action for the post. If there's any problem, the <tt>create</tt> action just shows the <tt>new</tt> view a second time, with any error messages.</p></div>
<div class="para"><p>Rails provides the <tt>flash</tt> hash (usually just called the Flash) so that messages can be carried over to another action, providing the user with useful information on the status of their request.  In the case of <tt>create</tt>, the user never actually sees any page rendered during the Post creation process, because it immediately redirects to the new Post as soon Rails saves the record. The Flash carries over a message to the next action, so that when the user is redirected back to the <tt>show</tt> action, they are presented with a message saying "Post was successfully created."</p></div>
<h3 id="_showing_an_individual_post">6.10. Showing an Individual Post</h3>
<div class="para"><p>When you click the <tt>show</tt> link for a post on the index page, it will bring you to a URL like <tt>http://localhost:3000/posts/1</tt>. Rails interprets this as a call to the <tt>show</tt> action for the resource, and passes in <tt>1</tt> as the <tt>:id</tt> parameter. Here's the <tt>show</tt> action:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">def</span></span> show
  <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>

  respond_to <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>format<span style="color: #990000">|</span>
    format<span style="color: #990000">.</span>html <span style="font-style: italic"><span style="color: #9A1900"># show.html.erb</span></span>
    format<span style="color: #990000">.</span>xml  <span style="color: #FF0000">{</span> render <span style="color: #990000">:</span>xml <span style="color: #990000">=&gt;</span> <span style="color: #009900">@post</span> <span style="color: #FF0000">}</span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>The <tt>show</tt> action uses <tt>Post.find</tt> to search for a single record in the database by its id value. After finding the record, Rails displays it by using <tt>show.html.erb</tt>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;p&gt;</span>
  <span style="color: #FF0000">&lt;b&gt;</span>Name<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
  <span style="color: #FF0000">&lt;%=h @post.name %&gt;</span>
<span style="color: #FF0000">&lt;/p&gt;</span>

<span style="color: #FF0000">&lt;p&gt;</span>
  <span style="color: #FF0000">&lt;b&gt;</span>Title<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
  <span style="color: #FF0000">&lt;%=h @post.title %&gt;</span>
<span style="color: #FF0000">&lt;/p&gt;</span>

<span style="color: #FF0000">&lt;p&gt;</span>
  <span style="color: #FF0000">&lt;b&gt;</span>Content<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
  <span style="color: #FF0000">&lt;%=h @post.content %&gt;</span>
<span style="color: #FF0000">&lt;/p&gt;</span>


<span style="color: #FF0000">&lt;%= link_to 'Edit', edit_post_path(@post) %&gt;</span> <span style="color: #990000">|</span>
<span style="color: #FF0000">&lt;%= link_to 'Back', posts_path %&gt;</span>
</tt></pre></div></div>
<h3 id="_editing_posts">6.11. Editing Posts</h3>
<div class="para"><p>Like creating a new post, editing a post is a two-part process. The first step is a request to <tt>edit_post_path(@post)</tt> with a particular post. This calls the <tt>edit</tt> action in the controller:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">def</span></span> edit
  <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>After finding the requested post, Rails uses the <tt>edit.html.erb</tt> view to display it:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>Editing post<span style="color: #FF0000">&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;% form_for(@post) do |f| %&gt;</span>
  <span style="color: #FF0000">&lt;%= f.error_messages %&gt;</span>

  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :name %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_field :name %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :title %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_field :title %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :content %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_area :content %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.submit "Update" %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
<span style="color: #FF0000">&lt;% end %&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'Show', @post %&gt;</span> <span style="color: #990000">|</span>
<span style="color: #FF0000">&lt;%= link_to 'Back', posts_path %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>Submitting the form created by this view will invoke the <tt>update</tt> action within the controller:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">def</span></span> update
  <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>

  respond_to <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>format<span style="color: #990000">|</span>
    <span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #009900">@post</span><span style="color: #990000">.</span>update_attributes<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>post<span style="color: #990000">])</span>
      flash<span style="color: #990000">[:</span>notice<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">'Post was successfully updated.'</span>
      format<span style="color: #990000">.</span>html <span style="color: #FF0000">{</span> redirect_to<span style="color: #990000">(</span><span style="color: #009900">@post</span><span style="color: #990000">)</span> <span style="color: #FF0000">}</span>
      format<span style="color: #990000">.</span>xml  <span style="color: #FF0000">{</span> head <span style="color: #990000">:</span>ok <span style="color: #FF0000">}</span>
    <span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
      format<span style="color: #990000">.</span>html <span style="color: #FF0000">{</span> render <span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"edit"</span> <span style="color: #FF0000">}</span>
      format<span style="color: #990000">.</span>xml  <span style="color: #FF0000">{</span> render <span style="color: #990000">:</span>xml <span style="color: #990000">=&gt;</span> <span style="color: #009900">@post</span><span style="color: #990000">.</span>errors<span style="color: #990000">,</span> <span style="color: #990000">:</span>status <span style="color: #990000">=&gt;</span> <span style="color: #990000">:</span>unprocessable_entity <span style="color: #FF0000">}</span>
    <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>In the <tt>update</tt> action, Rails first uses the <tt>:id</tt> parameter passed back from the edit view to locate the database record that's being edited. The <tt>update_attributes</tt> call then takes the rest of the parameters from the request and applies them to this record. If all goes well, the user is redirected to the post's <tt>show</tt> view. If there are any problems, it's back to <tt>edit</tt> to correct them.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/note.png" alt="Note" />
</td>
<td class="content">Sharp-eyed readers will have noticed that the <tt>form_for</tt> declaration is identical for the <tt>new</tt> and <tt>edit</tt> views. Rails generates different code for the two forms because it's smart enough to notice that in the one case it's being passed a new record that has never been saved, and in the other case an existing record that has already been saved to the database. In a production Rails application, you would ordinarily eliminate this duplication by moving identical code to a <em>partial template</em>, which you could then include in both parent templates. But the scaffold generator tries not to make too many assumptions, and generates code that’s easy to modify if you want different forms for <tt>create</tt> and <tt>edit</tt>.</td>
</tr></table>
</div>
<h3 id="_destroying_a_post">6.12. Destroying a Post</h3>
<div class="para"><p>Finally, clicking one of the <tt>destroy</tt> links sends the associated id to the <tt>destroy</tt> action:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">def</span></span> destroy
  <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
  <span style="color: #009900">@post</span><span style="color: #990000">.</span>destroy

  respond_to <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>format<span style="color: #990000">|</span>
    format<span style="color: #990000">.</span>html <span style="color: #FF0000">{</span> redirect_to<span style="color: #990000">(</span>posts_url<span style="color: #990000">)</span> <span style="color: #FF0000">}</span>
    format<span style="color: #990000">.</span>xml  <span style="color: #FF0000">{</span> head <span style="color: #990000">:</span>ok <span style="color: #FF0000">}</span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>The <tt>destroy</tt> method of an Active Record model instance removes the corresponding record from the database. After that's done, there isn't any record to display, so Rails redirects the user's browser to the index view for the model.</p></div>
</div>
<h2 id="_drying_up_the_code">7. DRYing up the Code</h2>
<div class="sectionbody">
<div class="para"><p>At this point, it’s worth looking at some of the tools that Rails provides to eliminate duplication in your code. In particular, you can use <em>partials</em> to clean up duplication in views and <em>filters</em> to help with duplication in controllers.</p></div>
<h3 id="_using_partials_to_eliminate_view_duplication">7.1. Using Partials to Eliminate View Duplication</h3>
<div class="para"><p>As you saw earlier, the scaffold-generated views for the <tt>new</tt> and <tt>edit</tt> actions are largely identical. You can pull the shared code out into a <tt>partial</tt> template. This requires editing the new and edit views, and adding a new template:</p></div>
<div class="para"><p><tt>new.html.erb</tt>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>New post<span style="color: #FF0000">&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;%= render :partial =&gt;</span> <span style="color: #FF0000">"form"</span> <span style="color: #990000">%&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'Back', posts_path %&gt;</span>
</tt></pre></div></div>
<div class="para"><p><tt>edit.html.erb</tt>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>Editing post<span style="color: #FF0000">&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;%= render :partial =&gt;</span> <span style="color: #FF0000">"form"</span> <span style="color: #990000">%&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'Show', @post %&gt;</span> <span style="color: #990000">|</span>
<span style="color: #FF0000">&lt;%= link_to 'Back', posts_path %&gt;</span>
</tt></pre></div></div>
<div class="para"><p><tt>_form.html.erb</tt>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;% form_for(@post) do |f| %&gt;</span>
  <span style="color: #FF0000">&lt;%= f.error_messages %&gt;</span>

  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :name %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_field :name %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :title, "title" %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_field :title %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :content %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_area :content %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.submit "Save" %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
<span style="color: #FF0000">&lt;% end %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>Now, when Rails renders the <tt>new</tt> or <tt>edit</tt> view, it will insert the <tt>_form</tt> partial at the indicated point. Note the naming convention for partials: if you refer to a partial named <tt>form</tt> inside of a view, the corresponding file is <tt>_form.html.erb</tt>, with a leading underscore.</p></div>
<div class="para"><p>For more information on partials, refer to the <a href="../layouts_and_rendering.html">Layouts and Rending in Rails</a> guide.</p></div>
<h3 id="_using_filters_to_eliminate_controller_duplication">7.2. Using Filters to Eliminate Controller Duplication</h3>
<div class="para"><p>At this point, if you look at the controller for posts, you’ll see some duplication:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> PostsController <span style="color: #990000">&lt;</span> ApplicationController
  <span style="font-style: italic"><span style="color: #9A1900"># ...</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> show
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
        <span style="font-style: italic"><span style="color: #9A1900"># ...</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> edit
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> update
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
    <span style="font-style: italic"><span style="color: #9A1900"># ...</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> destroy
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
    <span style="font-style: italic"><span style="color: #9A1900"># ...</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>Four instances of the exact same line of code doesn’t seem very DRY. Rails provides <em>filters</em> as a way to address this sort of repeated code. In this case, you can DRY things up by using a <tt>before_filter</tt>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> PostsController <span style="color: #990000">&lt;</span> ApplicationController
  before_filter <span style="color: #990000">:</span>find_post<span style="color: #990000">,</span> <span style="color: #990000">:</span>only <span style="color: #990000">=&gt;</span> <span style="color: #990000">[:</span>show<span style="color: #990000">,</span> <span style="color: #990000">:</span>edit<span style="color: #990000">,</span> <span style="color: #990000">:</span>update<span style="color: #990000">,</span> <span style="color: #990000">:</span>destroy<span style="color: #990000">]</span>
  <span style="font-style: italic"><span style="color: #9A1900"># ...</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> show
        <span style="font-style: italic"><span style="color: #9A1900"># ...</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> edit
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> update
    <span style="font-style: italic"><span style="color: #9A1900"># ...</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> destroy
    <span style="font-style: italic"><span style="color: #9A1900"># ...</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  private
    <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> find_post
      <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
    <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>Rails runs <em>before filters</em> before any action in the controller. You can use the <tt>:only</tt> clause to limit a before filter to only certain actions, or an <tt>:except</tt> clause to specifically skip a before filter for certain actions. Rails also allows you to define <em>after filters</em> that run after processing an action, as well as <em>around filters</em> that surround the processing of actions. Filters can also be defined in external classes to make it easy to share them between controllers.</p></div>
<div class="para"><p>For more information on filters, see the <a href="actioncontroller_basics.html">Action Controller Basics</a> guide.</p></div>
</div>
<h2 id="_adding_a_second_model">8. Adding a Second Model</h2>
<div class="sectionbody">
<div class="para"><p>Now that you've seen what's in a model built with scaffolding, it's time to add a second model to the application. The second model will handle comments on blog posts.</p></div>
<h3 id="_generating_a_model">8.1. Generating a Model</h3>
<div class="para"><p>Models in Rails use a singular name, and their corresponding database tables use a plural name. For the model to hold comments, the convention is to use the name Comment. Even if you don't want to use the entire apparatus set up by scaffolding, most Rails developers still use generators to make things like models and controllers. To create the new model, run this command in your terminal:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ script/generate model Comment commenter<span style="color: #990000">:</span>string body<span style="color: #990000">:</span>text post<span style="color: #990000">:</span>references
</tt></pre></div></div>
<div class="para"><p>This command will generate four files:</p></div>
<div class="ilist"><ul>
<li>
<p>
<tt>app/models/comment.rb</tt> - The model
</p>
</li>
<li>
<p>
+db/migrate/20081013214407_create_comments.rb - The migration
</p>
</li>
<li>
<p>
<tt>test/unit/comment_test.rb</tt> and <tt>test/fixtures/comments.yml</tt> - The test harness.
</p>
</li>
</ul></div>
<div class="para"><p>First, take a look at <tt>comment.rb</tt>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> Comment <span style="color: #990000">&lt;</span> ActiveRecord<span style="color: #990000">::</span>Base
  belongs_to <span style="color: #990000">:</span>post
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>This is very similar to the <tt>post.rb</tt> model that you saw earlier. The difference is the line <tt>belongs_to :post</tt>, which sets up an Active Record <em>association</em>. You'll learn a little about associations in the next section of this guide.</p></div>
<div class="para"><p>In addition to the model, Rails has also made a migration to create the corresponding database table:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> CreateComments <span style="color: #990000">&lt;</span> ActiveRecord<span style="color: #990000">::</span>Migration
  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> <span style="font-weight: bold"><span style="color: #0000FF">self</span></span><span style="color: #990000">.</span>up
    create_table <span style="color: #990000">:</span>comments <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>t<span style="color: #990000">|</span>
      t<span style="color: #990000">.</span>string <span style="color: #990000">:</span>commenter
      t<span style="color: #990000">.</span>text <span style="color: #990000">:</span>body
      t<span style="color: #990000">.</span>references <span style="color: #990000">:</span>post

      t<span style="color: #990000">.</span>timestamps
    <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> <span style="font-weight: bold"><span style="color: #0000FF">self</span></span><span style="color: #990000">.</span>down
    drop_table <span style="color: #990000">:</span>comments
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>The <tt>t.references</tt> line sets up a foreign key column for the association between the two models. Go ahead and run the migration:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ rake db<span style="color: #990000">:</span>migrate
</tt></pre></div></div>
<div class="para"><p>Rails is smart enough to only execute the migrations that have not already been run against this particular database.</p></div>
<h3 id="_associating_models">8.2. Associating Models</h3>
<div class="para"><p>Active Record associations let you easily declare the relationship between two models. In the case of comments and posts, you could write out the relationships this way:</p></div>
<div class="ilist"><ul>
<li>
<p>
Each comment belongs to one post
</p>
</li>
<li>
<p>
One post can have many comments
</p>
</li>
</ul></div>
<div class="para"><p>In fact, this is very close to the syntax that Rails uses to declare this association. You've already seen the line of code inside the Comment model that makes each comment belong to a Post:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> Comment <span style="color: #990000">&lt;</span> ActiveRecord<span style="color: #990000">::</span>Base
  belongs_to <span style="color: #990000">:</span>post
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>You'll need to edit the <tt>post.rb</tt> file to add the other side of the association:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> Post <span style="color: #990000">&lt;</span> ActiveRecord<span style="color: #990000">::</span>Base
  validates_presence_of <span style="color: #990000">:</span>name<span style="color: #990000">,</span> <span style="color: #990000">:</span>title
  validates_length_of <span style="color: #990000">:</span>title<span style="color: #990000">,</span> <span style="color: #990000">:</span>minimum <span style="color: #990000">=&gt;</span> <span style="color: #993399">5</span>
  has_many <span style="color: #990000">:</span>comments
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>These two declarations enable a good bit of automatic behavior. For example, if you have an instance variable <tt>@post</tt> containing a post, you can retrieve all the comments belonging to that post as the array <tt>@post.comments</tt>.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">For more information on Active Record associations, see the <a href="../association_basics.html">Active Record Associations</a> guide.</td>
</tr></table>
</div>
<h3 id="_adding_a_route">8.3. Adding a Route</h3>
<div class="para"><p><em>Routes</em> are entries in the <tt>config/routes.rb</tt> file that tell Rails how to match incoming HTTP requests to controller actions. Open up that file and find the existing line referring to <tt>posts</tt>. Then edit it as follows:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>map<span style="color: #990000">.</span>resources <span style="color: #990000">:</span>posts <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>post<span style="color: #990000">|</span>
  post<span style="color: #990000">.</span>resources <span style="color: #990000">:</span>comments
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>This creates <tt>comments</tt> as a <em>nested resource</em> within <tt>posts</tt>. This is another part of capturing the hierarchical relationship that exists between posts and comments.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">For more information on routing, see the <a href="../routing_outside_in">Rails Routing from the Outside In</a> guide.</td>
</tr></table>
</div>
<h3 id="_generating_a_controller">8.4. Generating a Controller</h3>
<div class="para"><p>With the model in hand, you can turn your attention to creating a matching controller. Again, there's a generator for this:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ script/generate controller Comments index show new edit
</tt></pre></div></div>
<div class="para"><p>This creates seven files:</p></div>
<div class="ilist"><ul>
<li>
<p>
<tt>app/controllers/comments_controller.rb</tt> - The controller
</p>
</li>
<li>
<p>
<tt>app/helpers/comments_helper.rb</tt> - A view helper file
</p>
</li>
<li>
<p>
<tt>app/views/comments/index.html.erb</tt> - The view for the index action
</p>
</li>
<li>
<p>
<tt>app/views/comments/show.html.erb</tt> - The view for the show action
</p>
</li>
<li>
<p>
<tt>app/views/comments/new.html.erb</tt> - The view for the new action
</p>
</li>
<li>
<p>
<tt>app/views/comments/edit.html.erb</tt> - The view for the edit action
</p>
</li>
<li>
<p>
<tt>test/functional/comments_controller_test.rb</tt> - The functional tests for the controller
</p>
</li>
</ul></div>
<div class="para"><p>The controller will be generated with empty methods for each action that you specified in the call to <tt>script/generate controller</tt>:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> CommentsController <span style="color: #990000">&lt;</span> ApplicationController
  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> index
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> show
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> new
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> edit
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>You'll need to flesh this out with code to actually process requests appropriately in each method. Here's a version that (for simplicity's sake) only responds to requests that require HTML:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">class</span></span> CommentsController <span style="color: #990000">&lt;</span> ApplicationController
  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> index
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>post_id<span style="color: #990000">])</span>
    <span style="color: #009900">@comments</span> <span style="color: #990000">=</span> <span style="color: #009900">@post</span><span style="color: #990000">.</span>comments
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> show
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>post_id<span style="color: #990000">])</span>
    <span style="color: #009900">@comment</span> <span style="color: #990000">=</span> Comment<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> new
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>post_id<span style="color: #990000">])</span>
    <span style="color: #009900">@comment</span> <span style="color: #990000">=</span> <span style="color: #009900">@post</span><span style="color: #990000">.</span>comments<span style="color: #990000">.</span>build
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> create
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>post_id<span style="color: #990000">])</span>
    <span style="color: #009900">@comment</span> <span style="color: #990000">=</span> <span style="color: #009900">@post</span><span style="color: #990000">.</span>comments<span style="color: #990000">.</span>build<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>comment<span style="color: #990000">])</span>
    <span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #009900">@comment</span><span style="color: #990000">.</span>save
      redirect_to post_comment_path<span style="color: #990000">(</span><span style="color: #009900">@post</span><span style="color: #990000">,</span> <span style="color: #009900">@comment</span><span style="color: #990000">)</span>
    <span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
      render <span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"new"</span>
    <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> edit
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>post_id<span style="color: #990000">])</span>
    <span style="color: #009900">@comment</span> <span style="color: #990000">=</span> Comment<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

  <span style="font-weight: bold"><span style="color: #0000FF">def</span></span> update
    <span style="color: #009900">@post</span> <span style="color: #990000">=</span> Post<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>post_id<span style="color: #990000">])</span>
    <span style="color: #009900">@comment</span> <span style="color: #990000">=</span> Comment<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
    <span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #009900">@comment</span><span style="color: #990000">.</span>update_attributes<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>comment<span style="color: #990000">])</span>
      redirect_to post_comment_path<span style="color: #990000">(</span><span style="color: #009900">@post</span><span style="color: #990000">,</span> <span style="color: #009900">@comment</span><span style="color: #990000">)</span>
    <span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
      render <span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"edit"</span>
    <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
  <span style="font-weight: bold"><span style="color: #0000FF">end</span></span>

<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>You'll see a bit more complexity here than you did in the controller for posts. That's a side-effect of the nesting that you've set up; each request for a comment has to keep track of the post to which the comment is attached.</p></div>
<div class="para"><p>In addition, the code takes advantage of some of the methods available for an association. For example, in the <tt>new</tt> method, it calls</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #009900">@comment</span> <span style="color: #990000">=</span> <span style="color: #009900">@post</span><span style="color: #990000">.</span>comments<span style="color: #990000">.</span>build
</tt></pre></div></div>
<div class="para"><p>This creates a new <tt>Comment</tt> object <em>and</em> sets up the <tt>post_id</tt> field to have the <tt>id</tt> from the specified <tt>Post</tt> object in a single operation.</p></div>
<h3 id="_building_views">8.5. Building Views</h3>
<div class="para"><p>Because you skipped scaffolding, you'll need to build views for comments "by hand." Invoking <tt>script/generate controller</tt> will give you skeleton views, but they'll be devoid of actual content. Here's a first pass at fleshing out the comment views.</p></div>
<div class="para"><p>The <tt>index.html.erb</tt> view:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>Comments <span style="font-weight: bold"><span style="color: #0000FF">for</span></span> <span style="color: #FF0000">&lt;%= @post.title %&gt;&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;table&gt;</span>
  <span style="color: #FF0000">&lt;tr&gt;</span>
    <span style="color: #FF0000">&lt;th&gt;</span>Commenter<span style="color: #FF0000">&lt;/th&gt;</span>
    <span style="color: #FF0000">&lt;th&gt;</span>Body<span style="color: #FF0000">&lt;/th&gt;</span>
  <span style="color: #FF0000">&lt;/tr&gt;</span>

<span style="color: #FF0000">&lt;% for comment in @comments %&gt;</span>
  <span style="color: #FF0000">&lt;tr&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%=h comment.commenter %&gt;&lt;/td&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%=h comment.body %&gt;&lt;/td&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%= link_to 'Show', post_comment_path(@post, comment) %&gt;&lt;/td&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%= link_to 'Edit', edit_post_comment_path(@post, comment) %&gt;&lt;/td&gt;</span>
    <span style="color: #FF0000">&lt;td&gt;&lt;%= link_to 'Destroy', post_comment_path(@post, comment), :confirm =&gt;</span> <span style="color: #FF0000">'Are you sure?'</span><span style="color: #990000">,</span> <span style="color: #990000">:</span>method <span style="color: #990000">=&gt;</span> <span style="color: #990000">:</span>delete <span style="color: #990000">%&gt;</span><span style="color: #FF0000">&lt;/td&gt;</span>
  <span style="color: #FF0000">&lt;/tr&gt;</span>
<span style="color: #FF0000">&lt;% end %&gt;</span>
<span style="color: #FF0000">&lt;/table&gt;</span>

<span style="color: #FF0000">&lt;br /&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'New comment', new_post_comment_path(@post) %&gt;</span>
<span style="color: #FF0000">&lt;%= link_to 'Back to Post', @post %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>The <tt>new.html.erb</tt> view:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>New comment<span style="color: #FF0000">&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;% form_for([@post, @comment]) do |f| %&gt;</span>
  <span style="color: #FF0000">&lt;%= f.error_messages %&gt;</span>

  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :commenter %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_field :commenter %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :body %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_area :body %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.submit "Create" %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
<span style="color: #FF0000">&lt;% end %&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'Back', post_comments_path(@post) %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>The <tt>show.html.erb</tt> view:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>Comment on <span style="color: #FF0000">&lt;%= @post.title %&gt;&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;p&gt;</span>
  <span style="color: #FF0000">&lt;b&gt;</span>Commenter<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
  <span style="color: #FF0000">&lt;%=h @comment.commenter %&gt;</span>
<span style="color: #FF0000">&lt;/p&gt;</span>

<span style="color: #FF0000">&lt;p&gt;</span>
  <span style="color: #FF0000">&lt;b&gt;</span>Comment<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
  <span style="color: #FF0000">&lt;%=h @comment.body %&gt;</span>
<span style="color: #FF0000">&lt;/p&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'Edit', edit_post_comment_path(@post, @comment) %&gt;</span> <span style="color: #990000">|</span>
<span style="color: #FF0000">&lt;%= link_to 'Back', post_comments_path(@post) %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>The <tt>edit.html.erb</tt> view:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;h1&gt;</span>Editing comment<span style="color: #FF0000">&lt;/h1&gt;</span>

<span style="color: #FF0000">&lt;% form_for([@post, @comment]) do |f| %&gt;</span>
  <span style="color: #FF0000">&lt;%= f.error_messages %&gt;</span>

  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :commenter %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_field :commenter %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.label :body %&gt;&lt;br /&gt;</span>
    <span style="color: #FF0000">&lt;%= f.text_area :body %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
  <span style="color: #FF0000">&lt;p&gt;</span>
    <span style="color: #FF0000">&lt;%= f.submit "Update" %&gt;</span>
  <span style="color: #FF0000">&lt;/p&gt;</span>
<span style="color: #FF0000">&lt;% end %&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'Show', post_comment_path(@post, @comment) %&gt;</span> <span style="color: #990000">|</span>
<span style="color: #FF0000">&lt;%= link_to 'Back', post_comments_path(@post) %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>Again, the added complexity here (compared to the views you saw for managing comments) comes from the necessity of juggling a post and its comments at the same time.</p></div>
<h3 id="_hooking_comments_to_posts">8.6. Hooking Comments to Posts</h3>
<div class="para"><p>As a final step, I'll modify the <tt>show.html.erb</tt> view for a post to show the comments on that post, and to allow managing those comments:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #FF0000">&lt;p&gt;</span>
  <span style="color: #FF0000">&lt;b&gt;</span>Name<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
  <span style="color: #FF0000">&lt;%=h @post.name %&gt;</span>
<span style="color: #FF0000">&lt;/p&gt;</span>

<span style="color: #FF0000">&lt;p&gt;</span>
  <span style="color: #FF0000">&lt;b&gt;</span>Title<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
  <span style="color: #FF0000">&lt;%=h @post.title %&gt;</span>
<span style="color: #FF0000">&lt;/p&gt;</span>

<span style="color: #FF0000">&lt;p&gt;</span>
  <span style="color: #FF0000">&lt;b&gt;</span>Content<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
  <span style="color: #FF0000">&lt;%=h @post.content %&gt;</span>
<span style="color: #FF0000">&lt;/p&gt;</span>

<span style="color: #FF0000">&lt;h2&gt;</span>Comments<span style="color: #FF0000">&lt;/h2&gt;</span>
<span style="color: #FF0000">&lt;% @post.comments.each do |c| %&gt;</span>
        <span style="color: #FF0000">&lt;p&gt;</span>
          <span style="color: #FF0000">&lt;b&gt;</span>Commenter<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
          <span style="color: #FF0000">&lt;%=h c.commenter %&gt;</span>
        <span style="color: #FF0000">&lt;/p&gt;</span>

        <span style="color: #FF0000">&lt;p&gt;</span>
          <span style="color: #FF0000">&lt;b&gt;</span>Comment<span style="color: #990000">:</span><span style="color: #FF0000">&lt;/b&gt;</span>
          <span style="color: #FF0000">&lt;%=h c.body %&gt;</span>
        <span style="color: #FF0000">&lt;/p&gt;</span>
<span style="color: #FF0000">&lt;% end %&gt;</span>

<span style="color: #FF0000">&lt;%= link_to 'Edit', edit_post_path(@post) %&gt;</span> <span style="color: #990000">|</span>
<span style="color: #FF0000">&lt;%= link_to 'Back', posts_path %&gt;</span>
<span style="color: #FF0000">&lt;%= link_to 'Manage Comments', post_comments_path(@post) %&gt;</span>
</tt></pre></div></div>
<div class="para"><p>Note that each post has its own individual comments collection, accessible as <tt>@post.comments</tt>. That's a consequence of the declarative associations in the models. Path helpers such as <tt>post_comments_path</tt> come from the nested route declaration in <tt>config/routes.rb</tt>.</p></div>
</div>
<h2 id="_what_s_next">9. What's Next?</h2>
<div class="sectionbody">
<div class="para"><p>Now that you've seen your first Rails application, you should feel free to update it and experiment on your own. But you don't have to do everything without help. As you need assistance getting up and running with Rails, feel free to consult these support resources:</p></div>
<div class="ilist"><ul>
<li>
<p>
The <a href="http://manuals.rubyonrails.org/">Ruby On Rails guides</a>
</p>
</li>
<li>
<p>
The <a href="http://groups.google.com/group/rubyonrails-talk">Ruby on Rails mailing list</a>
</p>
</li>
<li>
<p>
The #rubyonrails channel on irc.freenode.net
</p>
</li>
<li>
<p>
The <a href="http://wiki.rubyonrails.org/rails">Rails wiki</a>
</p>
</li>
</ul></div>
<div class="para"><p>Rails also comes with built-in help that you can generate using the rake command-line utility:</p></div>
<div class="ilist"><ul>
<li>
<p>
Running <tt>rake doc:guides</tt> will put a full copy of the Rails Guides in the <tt>/doc/guides</tt> folder of your application. Open <tt>/doc/guides/index.html</tt> in your web browser to explore the Guides.
</p>
</li>
<li>
<p>
Running <tt>rake doc:rails</tt> will put a full copy of the API documentation for Rails in the <tt>/doc/api</tt> folder of your application. Open <tt>/doc/api/index.html</tt> in your web browser to explore the API documentation.
</p>
</li>
</ul></div>
</div>
<h2 id="_changelog">10. Changelog</h2>
<div class="sectionbody">
<div class="para"><p><a href="http://rails.lighthouseapp.com/projects/16213-rails-guides/tickets/2">Lighthouse ticket</a></p></div>
<div class="ilist"><ul>
<li>
<p>
November 3, 2008: Formatting patch from Dave Rothlisberger
</p>
</li>
<li>
<p>
November 1, 2008: First approved version by <a href="../authors.html#mgunderloy">Mike Gunderloy</a>
</p>
</li>
<li>
<p>
October 16, 2008: Revised based on feedback from Pratik Naik by <a href="../authors.html#mgunderloy">Mike Gunderloy</a> (not yet approved for publication)
</p>
</li>
<li>
<p>
October 13, 2008: First complete draft by <a href="../authors.html#mgunderloy">Mike Gunderloy</a> (not yet approved for publication)
</p>
</li>
<li>
<p>
October 12, 2008: More detail, rearrangement, editing by <a href="../authors.html#mgunderloy">Mike Gunderloy</a> (not yet approved for publication)
</p>
</li>
<li>
<p>
September 8, 2008: initial version by James Miller (not yet approved for publication)
</p>
</li>
</ul></div>
</div>

		</div>
	</div>
</body>
</html>