Hello
I am wondering why the outputs q1 and q2 below are not the same. Is it a
bug?
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
_relation_a_table = Table('relation_a', Base.metadata,
Column('id', Integer, primary_key=True),
Column('refno', Integer)
)
_relation_b_table = Table('relation_b', Base.metadata,
Column('id', Integer, primary_key=True),
ForeignKeyConstraint(['id'], ['relation_a.id'])
)
_relation_c_table = Table('relation_c', Base.metadata,
Column('id', Integer, primary_key=True),
ForeignKeyConstraint(['id'], ['relation_b.id'])
)
class RelationA(Base):
__table__ = _relation_a_table
class RelationB(Base):
__table__ = _relation_b_table
relation_a = relationship('RelationA',
innerjoin=True,
backref=backref('relation_b'))
class RelationC(Base):
__table__ = _relation_c_table
relation_b = relationship('RelationB',
innerjoin=True,
backref=backref('relation_c',
innerjoin=True,
lazy='joined'))
if __name__ == '__main__':
# Initialize database models
engine = create_engine('postgresql://xxx@localhost:5432/xxx')
Session = sessionmaker(bind=engine)
session = Session()
q1 = session.query(RelationA).\
options(joinedload(RelationA.relation_b))
q2 = session.query(RelationA).\
outerjoin(RelationA.relation_b).\
options(contains_eager(RelationA.relation_b))
print q1
print q2
# Actual and expected SQL output for q1:
# SELECT
# relation_a.id AS relation_a_id,
# relation_a.refno AS relation_a_refno,
# relation_b_1.id AS relation_b_1_id,
# relation_c_1.id AS relation_c_1_id
# FROM relation_a
# LEFT OUTER JOIN relation_b AS relation_b_1 ON relation_a.id =
relation_b_1.id
# LEFT OUTER JOIN relation_c AS relation_c_1 ON relation_b_1.id =
relation_c_1.id
# Actual SQL output for q2 (with JOIN):
# SELECT
# relation_a.id AS relation_a_id,
# relation_a.refno AS relation_a_refno,
# relation_b.id AS relation_b_id,
# relation_c_1.id AS relation_c_1_id
# FROM relation_a
# LEFT OUTER JOIN relation_b ON relation_a.id = relation_b.id
# JOIN relation_c AS relation_c_1 ON relation_b.id = relation_c_1.id
# Expected SQL output for q2 (with LEFT OUTER JOIN):
# SELECT
# relation_a.id AS relation_a_id,
# relation_a.refno AS relation_a_refno,
# relation_b.id AS relation_b_id,
# relation_c_1.id AS relation_c_1_id
# FROM relation_a
# LEFT OUTER JOIN relation_b ON relation_a.id = relation_b.id
# LEFT OUTER JOIN relation_c AS relation_c_1 ON relation_b.id =
relation_c_1.id
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