Forked from dpwrussell/sqlalchemy_subqueryload_poly.py
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August 15, 2016 15:44
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SQLAlchemy Subqueryload Poly
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from sqlalchemy.ext.declarative import declarative_base | |
from sqlalchemy.orm import (relationship, sessionmaker, subqueryload, | |
with_polymorphic) | |
from sqlalchemy import create_engine, Column, String, Integer | |
from sqlalchemy.schema import ForeignKey | |
Base = declarative_base() | |
class A(Base): | |
__tablename__ = 't_a' | |
id = Column(Integer, primary_key=True) | |
class B(Base): | |
__tablename__ = 't_b' | |
type = Column(String(2)) | |
__mapper_args__ = { | |
'polymorphic_identity': 'b', | |
'polymorphic_on': type | |
} | |
id = Column(Integer, primary_key=True) | |
# Relationship to A | |
a_id = Column(Integer, ForeignKey('t_a.id')) | |
a = relationship('A', backref='bs') | |
class B2(B): | |
__tablename__ = 't_b2' | |
__mapper_args__ = { | |
'polymorphic_identity': 'b2', | |
} | |
id = Column(Integer, ForeignKey('t_b.id'), primary_key=True) | |
class C(Base): | |
__tablename__ = 't_c' | |
type = Column(String(2)) | |
__mapper_args__ = { | |
'polymorphic_identity': 'c', | |
'polymorphic_on': type | |
} | |
id = Column(Integer, primary_key=True) | |
# Relationship to B | |
b_id = Column(Integer, ForeignKey('t_b.id')) | |
b = relationship('B', backref='cs') | |
class C2(C): | |
__tablename__ = 't_c2' | |
__mapper_args__ = { | |
'polymorphic_identity': 'c2', | |
} | |
id = Column(Integer, ForeignKey('t_c.id'), primary_key=True) | |
class D(Base): | |
__tablename__ = 't_d' | |
id = Column(Integer, primary_key=True) | |
# Relationship to B | |
c_id = Column(Integer, ForeignKey('t_c.id')) | |
c = relationship('C', backref='ds') | |
engine = create_engine('sqlite://', echo=True) | |
Base.metadata.drop_all(engine) | |
Base.metadata.create_all(engine) | |
Session = sessionmaker(bind=engine) | |
session = Session() | |
for i in xrange(2): | |
a = A() | |
session.add(a) | |
b = B2(a=a) | |
session.add(b) | |
c = C2(b=b) | |
session.add(c) | |
d = D(c=c) | |
session.add(d) | |
session.commit() | |
b_b2 = with_polymorphic(B, [B2], flat=True) | |
c_c2 = with_polymorphic(C, [C2], flat=True) | |
# Broken -- the query on D has a cross join between | |
# (A join B) and (B join C join D). | |
r = session.query( | |
A | |
).options( | |
subqueryload( | |
A.bs.of_type(b_b2) | |
).subqueryload( | |
b_b2.cs.of_type(c_c2) | |
).subqueryload( | |
c_c2.ds | |
) | |
).all() | |
# Note that the output is correct even though the generated query is wrong. | |
for a in r: | |
print a.id | |
for b in a.bs: | |
print '\t', b.id | |
for c in b.cs: | |
print '\t\t', c.id | |
for d in c.ds: | |
print '\t\t\t', d.id |
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