[Sqlalchemy-tickets] Issue #4327: Expire on delete (was not expired before) (zzzeek/sqlalchemy)

[Dmytro S. <iss...@bi...>]

New issue 4327: Expire on delete (was not expired before)
https://bitbucket.org/zzzeek/sqlalchemy/issues/4327/expire-on-delete-was-not-expired-before

Dmytro Starosud:

Regression from 1.1.15 to 1.2.11. Maybe related to [this](https://docs.sqlalchemy.org/en/latest/changelog/changelog_12.html#change-21bf00984dcf04fa68883e4588196816).

Please consider following code snippet.

```
#!python
Base = declarative_base()


class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)

    children = relationship(
        'Child',
        foreign_keys='Child.parent_id', back_populates='parent', cascade='all, delete-orphan')

    first_child_id = Column(Integer, ForeignKey('child.id'))
    first_child = relationship('Child', foreign_keys=first_child_id, post_update=True)

    updated_at = Column(DateTime(), onupdate=func.now())


class Child(Base):
    __tablename__ = 'child'
    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey(Parent.id), nullable=False)
    parent = relationship(Parent, foreign_keys=parent_id, back_populates='children')


Base.metadata.create_all(session.bind, checkfirst=True)

child = Child()
parent = Parent(children=[child], first_child=child)
session.add(parent)
session.flush()
parent_id = parent.id
session.expunge_all()


@event.listens_for(Parent, 'expire')
def receive_expire(target, attrs):
    traceback.print_stack()


parent = session.query(Parent).get(parent_id)
session.delete(parent)
session.flush()

print(parent.updated_at)
```

With SQLAlchemy==1.1.15 it outputs `2018-08-23 12:06:19.291603`, nothing more and no failures.

With SQLAlchemy==1.2.11 it outputs two stack traces: one from expire event and one when trying access `parent.updated_at`.


```
#!console
  File "coze.py", line 62, in <module>
    session.flush()
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/session.py", line 2254, in flush
    self._flush(objects)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/session.py", line 2344, in _flush
    flush_context.execute()
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/unitofwork.py", line 391, in execute
    rec.execute(self)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/unitofwork.py", line 542, in execute
    persistence.post_update(self.mapper, states, uow, cols)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/persistence.py", line 234, in post_update
    mapper, table, update)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/persistence.py", line 975, in _emit_post_update_statements
    c, c.context.compiled_parameters[0])
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/persistence.py", line 1163, in _postfetch_post_update
    for c in postfetch_cols if c in
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/state.py", line 593, in _expire_attributes
    self.manager.dispatch.expire(self, attribute_names)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/event/attr.py", line 284, in __call__
    fn(*args, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/events.py", line 202, in wrap
    return fn(state.obj(), *arg, **kw)
  File "coze.py", line 57, in receive_expire
    traceback.print_stack()
Traceback (most recent call last):
  File "coze.py", line 64, in <module>
    print(parent.updated_at)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/attributes.py", line 242, in __get__
    return self.impl.get(instance_state(instance), dict_)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/attributes.py", line 594, in get
    value = state._load_expired(state, passive)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/state.py", line 608, in _load_expired
    self.manager.deferred_scalar_loader(self, toload)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/orm/loading.py", line 881, in load_scalar_attributes
    raise orm_exc.ObjectDeletedError(state)
sqlalchemy.orm.exc.ObjectDeletedError: Instance '<Parent at 0x7fa8177dc160>' has been deleted, or its row is otherwise not present.
```

Please clarify. Does this mean deleted instance cannot be used after flush any more?

Thanks a lot in advance.