Hello
I don't understand why the backref 'relation_b' of relationship
'relation_a' is not properly set when declaring 'relation_a'. Below is an
example that highlight this situation.
I must probably miss the philosophy being relation backref. What should I
do to get backref working from the beginning?
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)
)
_relation_b_table = Table('relation_b', Base.metadata,
Column('id', Integer, primary_key=True),
ForeignKeyConstraint(['id'], ['relation_a.id'])
)
class RelationA(Base):
__table__ = _relation_a_table
class RelationB(Base):
__table__ = _relation_b_table
relation_a = relationship('RelationA', backref='relation_b')
if __name__ == '__main__':
engine = create_engine('postgresql://xxxx@localhost:5432/xxxx')
Session = sessionmaker(bind=engine)
session = Session()
print RelationA.__dict__.has_key('relation_b')
q1 = session.query(RelationA).outerjoin(RelationA.relation_b)
print RelationA.__dict__.has_key('relation_b')
q2 = session.query(RelationA.id).outerjoin(RelationA.relation_b)
# Output:
# False
# True
# Output when q1 (line 31) is commented out:
# False
# False
# Traceback (most recent call last):
# File "/my_path/dummy.py", line 35, in <module>
# q2 = session.query(RelationA.id).outerjoin(RelationA.relation_b)
# AttributeError: type object 'RelationA' has no attribute 'relation_b'
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