[Sqlalchemy-tickets] Issue #3015: DELETEs executed twice when using history_meta and subclassing models (zzzeek/sqlalchemy)

[matt c. <iss...@bi...>]

New issue 3015: DELETEs executed twice when using history_meta and subclassing models
https://bitbucket.org/zzzeek/sqlalchemy/issue/3015/deletes-executed-twice-when-using

matt chisholm:

When using history_meta and also subclassing from model classes (which we do in order to add additional query parameters in our API), SQLAlchemy 0.9.4 raises an error about the number of rows that were deleted not matching the number of rows intended to be deleted. 

This bug is new in 0.9.4, it does not occur in 0.9.3 or 0.9.2. 

Attached is a minimal test case.

There is also a hack in here which fixes another bug, the `SubclassEquivalenceMixIn`. If you remove that from the base classes for `APIBar`, you can see why we are using that mix-in.

Here is the traceback:

```
2014-04-04 18:55:38,671 INFO sqlalchemy.engine.base.Engine DELETE FROM foo_bar WHERE foo_bar.foo_id = %(foo_id)s AND foo_bar.bar_id = %(bar_id)s
2014-04-04 18:55:38,671 INFO sqlalchemy.engine.base.Engine {'foo_id': 1, 'bar_id': 1}
2014-04-04 18:55:38,672 INFO sqlalchemy.engine.base.Engine DELETE FROM foo_bar WHERE foo_bar.foo_id = %(foo_id)s AND foo_bar.bar_id = %(bar_id)s
2014-04-04 18:55:38,672 INFO sqlalchemy.engine.base.Engine {'foo_id': 1, 'bar_id': 1}
2014-04-04 18:55:38,672 INFO sqlalchemy.engine.base.Engine ROLLBACK
Traceback (most recent call last):
  File "sqlalchemy-delete-bug.py", line 100, in <module>
    db.session.commit()
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/scoping.py", line 149, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 765, in commit
    self.transaction.commit()
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 370, in commit
    self._prepare_impl()
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 350, in _prepare_impl
    self.session.flush()
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 1903, in flush
    self._flush(objects)
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 2021, in _flush
    transaction.rollback(_capture_exception=True)
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 57, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 1985, in _flush
    flush_context.execute()
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/unitofwork.py", line 370, in execute
    rec.execute(self)
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/unitofwork.py", line 479, in execute
    self.dependency_processor.process_saves(uow, states)
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/dependency.py", line 1083, in process_saves
    secondary_update, secondary_delete)
  File "/Users/matt/.virtualenvs/sqlalchemy-delete-bug/lib/python2.7/site-packages/sqlalchemy/orm/dependency.py", line 1104, in _run_crud
    result.rowcount)
sqlalchemy.orm.exc.StaleDataError: DELETE statement on table 'foo_bar' expected to delete 1 row(s); Only 0 were matched.
```

I would not be the least bit surprised if either this code or flask-sqlalchemy were just doing something horribly stupid. 


Responsible: zzzeek