HSTORE adapter registration in psycopg2 conflicts with SQLAlchemy

djangonauts / django-hstore

PostgreSQL HStore support for Django.

http://django-hstore.readthedocs.io/

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HSTORE adapter registration in psycopg2 conflicts with SQLAlchemy #45

Closed gthb closed 10 years ago

gthb commented 10 years ago

If both django_hstore and SQLAlchemy are used in the same Python process with psycopg2, then django_hstore's adapter registration will cause psycopg2 to return HStoreDict instances to SQLAlchemy, which expects str. This causes errors like AttributeError: 'HStoreDict' object has no attribute 'decode' in sqlalchemy/dialects/postgresql/hstore.py:

    def process(value):
        if value is not None:
            return _parse_hstore(value.decode(encoding))

Some solution for the two to coexist would be good, for people who are using both Django and SQLAlchemy together.

One way might be to register the adapter only per connection/cursor, rather than globally (probably per cursor would be required for people using https://github.com/kennethreitz/django-postgrespool since the connections get shared).

niwinz commented 10 years ago

Hi!

Registering in each connection seems to be much overhead for normal use case, in my opinion, and per connection registering works well with connection pools because it register hstore on each connection retrieval from pool.

(With https://github.com/djangonauts/djorm-ext-pool works well and it not requires special backend...)

gthb commented 10 years ago

“Registering in each connection seems to be much overhead” — did you mean “in each cursor”?

I agree (if that's what you meant) that per-connection makes more sense. The main thing is to get rid of globally=True, to allow django_hstore to coexist with SQLAlchemy.