DjangoModelFactory's "_setup_next_sequence" assumes that pk is an integer

Offending code is here:

    @classmethod
    def _setup_next_sequence(cls):
        """Compute the next available PK, based on the 'pk' database field."""

        model = cls._associated_class  # pylint: disable=E1101
        manager = cls._get_manager(model)

        try:
            return 1 + manager.values_list('pk', flat=True
                ).order_by('-pk')[0]
        except IndexError:
            return 1

This problem didn’t exist in factory_boy 1.3. My field that was using a non-integer PK is using a sequence, which worked fine previously:

code = factory.Sequence(lambda n: str(n).zfill(3))

I haven’t dug into the code enough to know much about the changes that caused this problem, but ultimately I’d like to be able to use the sequence for the field again.

[wieczorek1990]

Thanks. After all I think like this is specific to the use case and everybody should write his own code.

[rbarrois]

No 😃

The goal of _setup_next_sequence() is simply to initialize the sequence counter, used in factory.Sequence() and factory.LazyAttributeSequence(). It holds no relation whatsoever with any database primary key — it has no knowledge thereof.

If you wish to have it start at a given value, why don’t you use Factory.reset_sequence()? Another option is to override the _setup_next_sequence() function in your factory to fetch a viable next ID from your database.

However, I strongly suggest letting your database generate the PK itself — otherwise, it is your job to define how your factory can choose values that are guaranteed not to conflict with those already existing in the DB. In your example, what happens if some part of the code under test creates an entry with PK “foo2” after the factory was called? There is no way for the factory to automagically guess that it has to move on to foo3…