regression in supporting reflection on PostgreSQL 8.4

In ..../postgresql/base.py a change was made ( ~~#3184~~, pull request bitbucket:30 ) to support additional smarts in reflecting indices and unique constraints in PostgreSQL. Unfortunately, this change is not compatible with PostgreSQL 8.4 which does not have a 'conindid' column.

While it's not elegant, I whipped up the following patch:

diff -ur SQLAlchemy-1.0.0b3.orig/lib/sqlalchemy/dialects/postgresql/base.py SQLAlchemy-1.0.0b3/lib/sqlalchemy/dialects/postgresql/base.py
--- SQLAlchemy-1.0.0b3.orig/lib/sqlalchemy/dialects/postgresql/base.py  2015-03-24 09:51:23.850734852 -0500
+++ SQLAlchemy-1.0.0b3/lib/sqlalchemy/dialects/postgresql/base.py   2015-03-24 09:59:38.201019680 -0500
@@ -2605,7 +2605,7 @@
           SELECT
               i.relname as relname,
               ix.indisunique, ix.indexprs, ix.indpred,
-              a.attname, a.attnum, c.conrelid, ix.indkey%s
+              a.attname, a.attnum, %s, ix.indkey%s
           FROM
               pg_class t
                     join pg_index ix on t.oid = ix.indrelid
@@ -2613,11 +2613,7 @@
                     left outer join
                         pg_attribute a
                         on t.oid = a.attrelid and %s
-                    left outer join
-                        pg_constraint c
-                        on (ix.indrelid = c.conrelid and
-                            ix.indexrelid = c.conindid and
-                            c.contype in ('p', 'u', 'x'))
+                    %s
           WHERE
               t.relkind IN ('r', 'v', 'f', 'm')
               and t.oid = :table_oid
@@ -2629,8 +2625,14 @@
             # version 8.3 here was based on observing the
             # cast does not work in PG 8.2.4, does work in 8.3.0.
             # nothing in PG changelogs regarding this.
+            "c.conrelid" if self.server_version_info >= (9, 0) else "NULL as conrelid",
             "::varchar" if self.server_version_info >= (8, 3) else "",
-            self._pg_index_any("a.attnum", "ix.indkey")
+            self._pg_index_any("a.attnum", "ix.indkey"),
+            """left outer join
+                        pg_constraint c
+                        on (ix.indrelid = c.conrelid and
+                            ix.indexrelid = c.conindid and
+                            c.contype in ('p', 'u', 'x'))""" if self.server_version_info >= (9, 0) else ""
         )

         t = sql.text(IDX_SQL, typemap={'attname': sqltypes.Unicode})

If you would prefer a pull request, I might be able to do that.

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