auto_now_add overrides factoryboy params

Say I have a model:

class Foo(models.Model):
    foo = models.DateField(auto_now_add=True)

with a trivial factory FooFactory, if I then do:

print FooFactory(foo=date(2001, 1, 1)).foo

it prints the current date, not the one I specified. To me this is a violation of principle of least surprise.

[rbarrois]

Hi,

That’s a built-in “feature” of Django: when a field has auto_now_add=True, Django will override any provided value with django.utils.timezone.now() ; this happens ‘‘after’’ factory_boy’s code runs.

You have two options:

1. Override your factory’ _create function:

class FooFactory(factory.django.DjangoModelFactory):
    FACTORY_FOR = models.Foo

    @classmethod
    def _create(cls, target_class, *args, **kwargs)
        foo = kwargs.pop('foo', None)
        obj = super(FooFactory, cls)._create(target_class, *args, **kwargs)
        if foo is not None:
            obj.foo = foo
            obj.save()
        return obj

1. Replace auto_now_add=True with the default keyword argument to models:

from django.utils import timezone

class Foo(models.Model):
    foo = models.DateField(default=timezone.now)

Note the lack of brackets in default=timezone.now; this could also be written as default=lambda: timezone.now() to be more explicit.

I have personnally chosen the second version, which lets me override created_at fields easily in tests.

[pymen]

Here is my way to do it in a universal way with freeze gun https://stackoverflow.com/a/70364787/1731460