[Sqlalchemy-tickets] Issue #2996: Could not locate any relevant foreign key columns with mixin and declared_attr (zzzeek/sqlalchemy)

[Charles-Axel D. <iss...@bi...>]

New issue 2996: Could not locate any relevant foreign key columns with mixin and declared_attr
https://bitbucket.org/zzzeek/sqlalchemy/issue/2996/could-not-locate-any-relevant-foreign-key

Charles-Axel Dein:

The following code:

```
#!python


from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy.orm import foreign
from sqlalchemy.orm import relationship
from sqlalchemy.orm import sessionmaker
from sqlalchemy.schema import Column, ForeignKey
from sqlalchemy.types import Integer, Boolean

Base = declarative_base()


class Transaction(Base):
    __tablename__ = 'transactions'
    id = Column(Integer, primary_key=True)
    invoice_id = Column(Integer, ForeignKey('invoices.id'))


class InvoiceMixin(object):

    __tablename__ = 'invoices'

    id = Column(Integer, primary_key=True)
    approved = Column(Boolean)

    @declared_attr
    def transactions(cls):
        return relationship(
            'Transaction',
            primaryjoin=lambda: Transaction.invoice_id == cls.id
            # primaryjoin=lambda: remote(Transaction.invoice_id) == cls.id
            # primaryjoin='Transaction.invoice_id == %s.id' % cls.__name__,
        )


class Invoice1(InvoiceMixin, Base):
    __table_args__ = {'extend_existing': True}


class Invoice2(InvoiceMixin, Base):
    __table_args__ = {'extend_existing': True}


def main():
    engine = create_engine('sqlite:///:memory:')
    Base.metadata.create_all(engine)
    Session = sessionmaker(bind=engine)
    session = Session()
    session.query(Invoice1).get(0)


if __name__ == '__main__':
    main()

```

Will fail with the following:


```
#!python

Traceback (most recent call last):
  File "reproduce_sqla_bug.py", line 53, in <module>
    main()
  File "reproduce_sqla_bug.py", line 49, in main
    session.query(Invoice1).get(0)
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 1151, in query
    return self._query_cls(entities, self, **kwargs)
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 106, in __init__
    self._set_entities(entities)
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 116, in _set_entities
    self._set_entity_selectables(self._entities)
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 149, in _set_entity_selectables
    ent.setup_entity(*d[entity])
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2980, in setup_entity
    self._with_polymorphic = ext_info.with_polymorphic_mappers
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 712, in __get__
    obj.__dict__[self.__name__] = result = self.fget(obj)
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 1840, in _with_polymorphic_mappers
    configure_mappers()
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 2544, in configure_mappers
    mapper._post_configure_properties()
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 1657, in _post_configure_properties
    prop.init()
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/interfaces.py", line 143, in init
    self.do_init()
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1512, in do_init
    self._setup_join_conditions()
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1588, in _setup_join_conditions
    can_be_synced_fn=self._columns_are_mapped
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1856, in __init__
    self._check_foreign_cols(self.primaryjoin, True)
  File "/Users/ca/.virtualenvs/sqlalchemy/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 2374, in _check_foreign_cols
    raise sa_exc.ArgumentError(err)
sqlalchemy.exc.ArgumentError: Could not locate any relevant foreign key columns for primary join condition 'transactions.invoice_id = invoices.id' on relationship Invoice1.transactions.  Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or are annotated in the join condition with the foreign() annotation.
```

If I don't specify the `primaryjoin`, it will be ok. If I remove one of the subclass (e.g. `Invoice1`), it will be ok. My guess is that this come from `_setup_pairs`'s deannotation step. The first time the relationship, it's gonna get rid of the annotation and the next time it runs, it won't have access to them. Actually, after having a second look, maybe it's not what's happening there. Am I missing anything?

Thanks a lot Mike!

Responsible: zzzeek