emit warning when Column is assigned directly to multiple names

[jerryji]

column_property hides original column from mapper when used with no change.

Results from running the attached column_property.py, tested against sqlalchemy git clone just now --

(sqlalchemy) C:\sqlalchemy>ipython
Python 2.7.5 (default, May 15 2013, 22:44:16) [v.1500 64 bit (AMD64)](MSC)

In [1](1): import sqlalchemy
In [2](2): sqlalchemy.__version__
Out[2](2): '0.9.0'

In [3](3): %run column_property.py
['id']('name_alias',)
['id', 'name']('name_alias',)

column_property.py (in case attachment fails), maybe not the right way to create an aliasing column, but still looks like a bug to me --

from sqlalchemy import (
    create_engine,
    Column,
    Text,
    Integer,
)
from sqlalchemy.orm import (
    scoped_session,
    sessionmaker,
    column_property,
)
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class NameMissing(Base):
    __tablename__ = 'name_missing'
    id = Column(Integer, primary_key=True)
    name = Column(Text)
    name_alias = column_property(name)

    def __init__(self, id, name):
        self.id = id
        self.name = name

class NameOK(Base):
    __tablename__ = 'name_ok'
    id = Column(Integer, primary_key=True)
    name = Column(Text)
    name_alias = column_property(name+'')

    def __init__(self, id, name):
        self.id = id
        self.name = name

engine = create_engine('sqlite://')
Base.metadata.create_all(engine)
dbsession = scoped_session(sessionmaker(bind=engine))
new_name_missing = NameMissing(1, 'foobar')
dbsession.add(new_name_missing)
new_name_ok = NameOK(1, 'foobar')
dbsession.add(new_name_ok)
dbsession.commit()

name_missing = dbsession.query(NameMissing).first()
print name_missing.__mapper__.columns.keys()

name_ok = dbsession.query(NameOK).first()
print name_ok.__mapper__.columns.keys()

Jerry

[Mike Bayer]

there's no bug here, the declaration of name = Column is equivalent of name_alias = column_property(Column), and an explicit column property trumps the plain column as you might be passing extra mapping options along. We can emit a warning for when this occurs, this patch is a start, needs some cleanup and tests:

diff --git a/lib/sqlalchemy/ext/declarative/base.py b/lib/sqlalchemy/ext/declarative/base.py
index 820c087..73723bc 100644
--- a/lib/sqlalchemy/ext/declarative/base.py
+++ b/lib/sqlalchemy/ext/declarative/base.py
@@ -14,7 +14,7 @@ from ... import util, exc
 from ...sql import expression
 from ... import event
 from . import clsregistry
-
+import collections

 def _declared_mapping_info(cls):
     # deferred mapping
@@ -173,15 +173,19 @@ def _as_declarative(cls, classname, dict_):

     # extract columns from the class dict
     declared_columns = set()
+    col_to_prop = collections.defaultdict(dict)
     for key, c in list(our_stuff.items()):
         if isinstance(c, (ColumnProperty, CompositeProperty)):
             for col in c.columns:
                 if isinstance(col, Column) and \
                     col.table is None:
                     _undefer_column_name(key, col)
+                    if isinstance(c, ColumnProperty):
+                        col_to_prop[col](col)[key](key) = c
                     declared_columns.add(col)
         elif isinstance(c, Column):
             _undefer_column_name(key, c)
+            col_to_prop[c](c)[key](key) = c
             declared_columns.add(c)
             # if the column is the same name as the key,
             # remove it from the explicit properties dict.
@@ -190,6 +194,10 @@ def _as_declarative(cls, classname, dict_):
             # in multi-column ColumnProperties.
             if key == c.key:
                 del our_stuff[key](key)
+    for col, entry in col_to_prop.items():
+        if len(entry) > 1:
+            util.warn("Column object named directly multiple times, "
+                "only one will be used: %s" % (", ".join(entry)))
     declared_columns = sorted(
         declared_columns, key=lambda c: c._creation_order)
     table = None
diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 4336c19..f828180 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -1218,7 +1218,6 @@ class Mapper(_InspectionAttr):
             self._log("Identified primary key columns: %s", primary_key)

     def _configure_properties(self):
-
         # Column and other ClauseElement objects which are mapped
         self.columns = self.c = util.OrderedProperties()

this also should probably try to detect if a straight Column is specified multiple times.

in this use case you want to be using synonym in order to produce a straight "alias" of a name.

[Mike Bayer]

more complete version detects any kind of name collision: de786a4208e621229769a8fb1f876f

[Mike Bayer]

Removing milestone: 0.9.0 (automated comment)