Calling bake_lazy_loaders() can raise IndexError

Hi! Apologies in advance if I'm missing something really obvious here. SQLAlchemy 1.0's BakedQuery feature is amazing! But I'm running into problems upon attempting to invoke bake_lazy_loaders() as described here. Here's an example (tested with SQLAlchemy 1.0.10 and 1.1.0b1.dev0):

from sqlalchemy import Column, Integer, ForeignKey, create_engine
from sqlalchemy.orm import Session, relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.baked import bake_lazy_loaders

bake_lazy_loaders()

Base = declarative_base()


class User(Base):
    __tablename__ = 'user'
    id = Column(Integer, primary_key=True)


class Address(Base):
    __tablename__ = 'address'
    id = Column(Integer, primary_key=True)
    user_id = Column(Integer, ForeignKey('user.id'))
    user = relationship("User", lazy='joined')


engine = create_engine('sqlite:///:memory:')
Base.metadata.create_all(engine)

session = Session(engine)
u = session.query(User).first()

This produces the following exception

  File "testcase.py", line 28, in <module>
    u = session.query(User).first()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1272, in query
    return self._query_cls(entities, self, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line 110, in __init__
    self._set_entities(entities)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line 120, in _set_entities
    self._set_entity_selectables(self._entities)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line 150, in _set_entity_selectables
    ent.setup_entity(*d[entity])
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line 3417, in setup_entity
    self._with_polymorphic = ext_info.with_polymorphic_mappers
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/util/langhelpers.py", line 747, in __get__
    obj.__dict__[self.__name__] = result = self.fget(obj)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/mapper.py", line 1893, in _with_polymorphic_mappers
    configure_mappers()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/mapper.py", line 2756, in configure_mappers
    mapper._post_configure_properties()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/mapper.py", line 1713, in _post_configure_properties
    prop.post_instrument_class(self)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/interfaces.py", line 526, in post_instrument_class
    self.strategy.init_class_attribute(mapper)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/strategies.py", line 1096, in init_class_attribute
    _get_strategy_by_cls(LazyLoader).init_class_attribute(mapper)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/interfaces.py", line 496, in _get_strategy_by_cls
    return self._get_strategy(cls._strategy_keys[0])
IndexError: list index out of range

It seems that the same exception is raised when the relationship is defined without lazy='joined', if bake_lazy_loaders() is invoked after the class mapping is defined.

Is this a bug, or am I misusing bake_lazy_loaders?

Comments (8)