Add support for BigAutoField

[hannseman]

It would be nice to have support for BigAutoField primary keys.

Would it be possible to just use the IntPacker for this field or do we have to introduce a LongPacker:

class LongPacker(object):
    @staticmethod
    def pack_pk(user_pk):
        return struct.pack(str("!l"), user_pk)

    @staticmethod
    def unpack_pk(data):
        return struct.unpack(str("!l"), data[:4])[0], data[4:]

[aaugustin]

You need 8 bytes for 64-bits integers in BigAutoField. This requires a new packer.

[aaugustin]

Oooooops — I was working on a patch on my end and didn't notice your pull request, which was perfectly correct, until I pushed my changes. Sorry :'(

[aaugustin]

It doesn't seem useful to run all tests in test_backends.py with all possible primary key types, but it may be interesting to run the most common ones: AutoField, BigAutoField, UUIDField. So I'm going to grab these changes from your PR.

[hannseman]

Oooooops — I was working on a patch on my end and didn't notice your pull request, which was perfectly correct, until I pushed my changes. Sorry :'(

No problem! I should've been clear about that I intended to create a PR. Thanks for the quick fix! 👍

[aaugustin]

FYI version 1.8 is released on PyPI with this feature.