[Sqlalchemy-tickets] Issue #3222: join to single-inh subclass without using a property-based join fails to apply single inh criterion (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3222: join to single-inh subclass without using a property-based join fails to apply single inh criterion
https://bitbucket.org/zzzeek/sqlalchemy/issue/3222/join-to-single-inh-subclass-without-using

Mike Bayer:


```
#!python

from sqlalchemy import Integer, ForeignKey, Column, String
from sqlalchemy.orm import Session, relationship
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    type = Column(String)
    cid = Column(ForeignKey('c.id'))
    c = relationship("C", backref="a")
    __mapper_args__ = {'polymorphic_on': type}


class B(A):
    __mapper_args__ = {'polymorphic_identity': 'b'}


class C(Base):
    __tablename__ = 'c'
    id = Column(Integer, primary_key=True)

s = Session()

print s.query(C, B).filter(C.id == B.cid)

print s.query(C, B).join(B, C.id == B.cid)

print s.query(C, B).join(B, C.a)

```

first query is OK:


```
#!sql

SELECT c.id AS c_id, a.id AS a_id, a.type AS a_type, a.cid AS a_cid 
FROM c, a 
WHERE c.id = a.cid AND a.type IN (:type_1)

```

second query lacks the discriminator:


```
#!sql

SELECT c.id AS c_id, a.id AS a_id, a.type AS a_type, a.cid AS a_cid 
FROM c JOIN a ON c.id = a.cid

```

third one is OK:


```
#!sql

SELECT c.id AS c_id, a.id AS a_id, a.type AS a_type, a.cid AS a_cid 
FROM c JOIN a ON c.id = a.cid AND a.type IN (:type_1)

```

the issue is the check inside of _join_entities assumes the ON clause was rendered orm.join() which also adds the criteria in.   So this patch resolves:


```
#!diff

diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index 7b2ea79..0c3bc26 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -1979,7 +1979,7 @@ class Query(object):
             info.selectable, \
             getattr(info, 'is_aliased_class', False)
 
-        if right_mapper:
+        if right_mapper and prop is not None:
             self._join_entities += (info, )
 
         if right_mapper and prop and \

```