DjangoModelFactory.build hits the database

[hannesstruss]

given this constellation:

class MyModel(models.Model):
    name = models.CharField(max_length=100)

class ModelFactory(DjangoModelFactory):
    FACTORY_FOR = MyModel

    name = 'John Doe'

class MyTestCase(TestCase):
    def test_factory(self):
        ModelFactory.build()

The test case will hit the database when generating an ID for the model (Stacktrace when using py.test that detects database usage in tests: https://gist.github.com/hannesstruss/f60e038daa588318ea57 )

I would expect .build() to not touch the database at all, but to create in-memory/test-local objects only. As far as I remember that was also how it worked before all Django-specific code was moved to DjangoModelFactory.

If this is expected, sorry for missing the memo :) What would be the best practice then to share code between a factory that does and one that doesn't save the model?

I tested in 2.2.1/Django 1.6.

[rbarrois]

Hi,

That's a recurring issue I have with the "auto-next-sequence" code, which I haven't gotten to fix yet : it requires a big rewrite of some internals to pass the "build or create" context around.

The simplest way to solve this would be to override the _generate_next_sequence to always return "1".

[anler]

Hi, one problem with that solution is that I'm using sequence to disambiguate unique fields (eg: username) and returning the same value for the sequence raises IntegrityError for these fields.

The best solution I could come with is just maintaining a global counter since I don't care what value the sequence has but that is unique everytime and leaves the database untouched:

    _SEQUENCE = 1
    _SEQUENCE_LOCK = threading.Lock()
    ...
    @classmethod
    def _setup_next_sequence(cls):
        with cls._SEQUENCE_LOCK:
            cls._SEQUENCE += 1
        return cls._SEQUENCE

[rbarrois]

This issue has been fixed in 13d310f, and will be part of the 2.5.0 release.