I encountered a little strangeness when joining to a class using single
table inheritance.
I was wondering why I got no results for one particular query.
This was originally encountered with PostgreSQL but was successfully
reproduced with SQLite.
Is this a bug or a user error?
----------------SNIP--------------------SNIP--------------------
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.engine import create_engine
from sqlalchemy.schema import Column, ForeignKey
from sqlalchemy.types import Integer, Unicode
from sqlalchemy.orm.session import Session
from sqlalchemy.orm import relationship
Base = declarative_base(create_engine('sqlite:///'))
class A(Base):
__tablename__ = 'a'
id = Column(Integer, primary_key=True)
disc = Column(Unicode, nullable=False)
name = Column(Unicode)
__mapper_args__ = {'polymorphic_on': disc}
class B(A):
__mapper_args__ = {'polymorphic_identity': 'b'}
class Z(Base):
__tablename__ = 'z'
id = Column(Integer, primary_key=True)
b_id = Column(Integer, ForeignKey(B.id))
b = relationship(B)
Base.metadata.create_all()
session = Session()
query = session.query(Z, A.name).outerjoin(Z.b).filter(Z.id == 1)
print query
#SELECT z.id AS z_id, z.b_id AS z_b_id, a.name AS a_name
#FROM z LEFT OUTER JOIN a ON a.id = z.b_id AND a.disc IN (?)
#WHERE z.id = ? AND a.disc IN (?)
# ^- why is this condition here?
#
# WORKAROUND:
# query = session.query(Z, A.name).outerjoin(Z.b).filter(Z.id == 1)
# ^- use the superclass instead
#
#SELECT z.id AS z_id, z.b_id AS z_b_id, a.name AS a_name
#FROM z LEFT OUTER JOIN a ON a.id = z.b_id AND a.disc IN (?)
#WHERE z.id = ?
# ^- no extra WHERE condition this time around
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