Sets in "in" lookups should be converted to list if backend doesn't support sets

[no]

Consider the following:

Model.objects.filter(pk__in = set([1, 1, 2, 3, 4, 3]))

If the backend is mysql, the generated SQL will contain WHERE id IN (1, 2, 3, 4). If the backend is postgresql there is an error: "can't adapt type 'set'".

Argument: switching between backends should not throw an error from the backend if the plain ORM (no backend-specific elements) is used.

I'm not sure where this belongs, but django shouldn't be throwing a backend error for this case.
Some potential fixes:

• Call list() on any iterable that's used for __in filters. (Preferable for me, should be non-breaking except in edge-cases)
• Disallow sets for all backends. (Enforces the same behaviour across all backends, but backward incompatible)
• Add adapter for sets to postgresql backend. (Might cause strange behaviour in cases where the set is used for other contexts)

[Tim Graham]

I couldn't reproduce with the attached test case. Does it fail for you? Can you provide a failing test case?

[no]

You're right. PEBKAC. The code that was throwing the error was an abstraction on top of using the raw cursor.execute, which doesn't adapt sets for pgsql, I was under the impression the abstraction used the django ORM.