[storm] Storm+twisted. store.invalidate() and sqllite

[Justin Warren]

I did some playing around with the twisted-integration branch of Storm
on the weekend, and it's really ace, so thanks heaps for all the work on
it.

One piece has me confused, though.

There's a monkey patch of storm.store.invalidate() to replace it with an
empty function. Unfortunately, this breaks lazy loading, and the use of
the __storm_loaded__ hook, which I find really handy and use quite a
bit.

The only reason I can find for this seems to be a test that fails
against a SQLite database:
tests.twistorm.DeferredStoreTestCase.test_find_and_rollback

This test fetches an object from the SQLite database, and then does a
rollback(). It then checks to see that the objects are still the same,
but if the original storm.store.invalidate() is left in, the test fails
with a sqlite error:

sqlite3.ProgrammingError: SQLite objects created in a thread can only be
used in that same thread.

I'm not sure I understand, but it seems that PySQLite does some wild and
crazy things with transactions, and Storm works around them by disabling
the dodgy hacks. I'm guessing that the way the twisted wrapper uses a
dedicated thread for the store access and its defer_to_thread() means
that objects grabbed from a store end up in the wrong thread somehow,
which causes this error.

Is this a SQLite only problem? If so, commenting out store.invalidate()
seems a bit heavy handed. The test comment seems to suggest that
commit() and rollback() have to be done manually with SQLite anyway, so
perhaps this means you need to know that you have to re-fetch the object
from the database manually, rather than rely on lazy-loading?

Sorry if I'm missing something obvious here. This is all deep-magic to
me.

-- 
Justin Warren <daedalus at eigenmagic.com>