Hi everyone!
I am trying to use the contains_eager option on a simple polymorphic query
that looks like:
class Superclass():
common_relationship = relationship('Common', ...)
discriminator_field = Column(String...)
__mapper_args__ = {'polymorphic_identity': 'superclass',
'polymorphic_on': discriminator_field}
class Subclass(Superclass):
fields...
poly = with_polymorphic(Superclass, '*')
db.session.query(poly).options(contains_eager(poly.common_relationship)).
join(poly.common_relationship).filter(Common.id == 1).all()
This code throws an error when I execute the query:
sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) subquery uses
ungrouped column "common.id" from outer query
Removing the contains_eager option and replacing it with a lazy or join
option does solve the problem, but introduces overhead to my SQL query.
What I am trying to achieve here is for the query to not perform two joins
(once for the join to filter on, and once for the join to populate the
poly.common_relationship field). Am I approaching this entirely wrong here?
Thanks in advance!
Jay
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