- Fixed a very old behavior where the lazy load emitted for a one-to-many

could inappropriately pull in the parent table, and also return results
inconsistent based on what's in the parent table, when the primaryjoin
includes some kind of discriminator against the parent table, such
as ``and_(parent.id == child.parent_id, parent.deleted == False)``.
While this primaryjoin doesn't make that much sense for a one-to-many,
it is slightly more common when applied to the many-to-one side, and
the one-to-many comes as a result of a backref.
Loading rows from ``child`` in this case would keep ``parent.deleted == False``
as is within the query, thereby yanking it into the FROM clause
and doing a cartesian product.  The new behavior will now substitute
the value of the local "parent.deleted" for that parameter as is
appropriate.   Though typically, a real-world app probably wants to use a
different primaryjoin for the o2m side in any case.
fixes #2948

1 files changed, 11 insertions, 4 deletions

diff --git a/lib/sqlalchemy/orm/relationships.py b/lib/sqlalchemy/orm/relationships.py
index a0b36ce57..311fba478 100644
--- a/lib/sqlalchemy/orm/relationships.py
+++ b/lib/sqlalchemy/orm/relationships.py
@@ -2587,6 +2587,7 @@ class JoinCondition(object):
         binds = util.column_dict()
         lookup = util.column_dict()
         equated_columns = util.column_dict()
+        being_replaced = set()
 
         if reverse_direction and self.secondaryjoin is None:
             for l, r in self.local_remote_pairs:
@@ -2594,16 +2595,22 @@ class JoinCondition(object):
                 _list.append((r, l))
                 equated_columns[l] = r
         else:
+            # replace all "local side" columns, which is
+            # anything that isn't marked "remote"
+            being_replaced.update(self.local_columns)
             for l, r in self.local_remote_pairs:
                 _list = lookup.setdefault(l, [])
                 _list.append((l, r))
                 equated_columns[r] = l
 
         def col_to_bind(col):
-            if col in lookup:
-                for tobind, equated in lookup[col]:
-                    if equated in binds:
-                        return None
+            if col in being_replaced or col in lookup:
+                if col in lookup:
+                    for tobind, equated in lookup[col]:
+                        if equated in binds:
+                            return None
+                else:
+                    assert not reverse_direction
                 if col not in binds:
                     binds[col] = sql.bindparam(
                         None, None, type_=col.type, unique=True)