[Sqlalchemy-tickets] Issue #4124: AbstractConcreteBase transmitting inappropriate "load only" props to expired relationship item (zzzeek/sqlalchemy)

[Michael B. <iss...@bi...>]

New issue 4124: AbstractConcreteBase transmitting inappropriate "load only" props to expired relationship item
https://bitbucket.org/zzzeek/sqlalchemy/issues/4124/abstractconcretebase-transmitting

Michael Bayer:

```
#!python

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import AbstractConcreteBase

Base = declarative_base()


class Abstract(AbstractConcreteBase, Base):
    pass

# using this base, no problem
# class Abstract(Base):
#    __abstract__ = True


class Concrete(Abstract):
    __tablename__ = 'concrete'

    id = Column(Integer, primary_key=True)

    details = relationship("Detail")


class Detail(Base):
    __tablename__ = 'detail'
    id = Column(Integer, primary_key=True)
    c2id = Column(ForeignKey('concrete.id'))


e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

s = Session(e)
s.add(Concrete(details=[Detail()]))
s.commit()

c1 = s.query(Concrete).first()

# triggers bug
s.expire(c1)


c1.details
```

trace, illustrates the pseudocolumn "type" is involved, also any other columns that get transmitted up to the base from other sibling classes end up here as well


```
#!

Traceback (most recent call last):
  File "test.py", line 44, in <module>
    c1.details
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/attributes.py", line 242, in __get__
    return self.impl.get(instance_state(instance), dict_)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/attributes.py", line 603, in get
    value = self.callable_(state, passive)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/strategies.py", line 623, in _load_for_state
    return self._emit_lazyload(session, state, ident_key, passive)
  File "<string>", line 1, in <lambda>
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/strategies.py", line 733, in _emit_lazyload
    lazy_clause, params = self._generate_lazy_clause(state, passive)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/strategies.py", line 556, in _generate_lazy_clause
    state, dict_, ident, passive)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/mapper.py", line 2609, in _get_state_attr_by_column
    return state.manager[prop.key].impl.get(state, dict_, passive=passive)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/attributes.py", line 598, in get
    value = state._load_expired(state, passive)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/state.py", line 594, in _load_expired
    self.manager.deferred_scalar_loader(self, toload)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 835, in load_scalar_attributes
    only_load_props=attribute_names)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 231, in load_on_ident
    return q.one()
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/query.py", line 2835, in one
    ret = self.one_or_none()
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/query.py", line 2805, in one_or_none
    ret = list(self)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 97, in instances
    util.raise_from_cause(err)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/util/compat.py", line 203, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 60, in instances
    for query_entity in query._entities
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/query.py", line 3720, in row_processor
    polymorphic_discriminator=self._polymorphic_discriminator
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 307, in _instance_processor
    mapper._props[k] for k in only_load_props)
  File "/home/classic/dev/sqlalchemy/lib/sqlalchemy/orm/loading.py", line 307, in <genexpr>
    mapper._props[k] for k in only_load_props)
KeyError: 'type'

```