auto_now_add overrides factoryboy params

[boxed]

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.

[l-astro]

Quick question - how should this be implemented for auto_add (rather than auto_add_now)? I have an "updated" field, but whether I use models.DateTimeField(auto_now=True) or override the django model .save() method, I can't seem to get FactoryBoy to return the correct value of updated (LazyAttribute(lambda o: o.created + timedelta(hours=1)) or using the _create() method) - it always returns timezone.now().

What's the best way to go here?

[rbarrois]

@lmannering I'm not sure about the issue you're having?

Basically:

• If you set auto_now on a Django field, the current value of the field will be overwritten when calling .save()
• Since that operation happens during the .save() step, its result cannot be seen in the factory (which operates before any instance of the model exists).

In other words, the way thinks work are:

1. factory_boy resolves all declarations into a set of values;
2. Those values are passed to MyModel.objects.create()
3. During the actual .save() from Django's core, the value of updated is replaced with timezone.now()

[l-astro]

Hi @rbarrois my fault, I wasn't particularly clear - my question is, given your two options on how to best circumvent auto_add_now when using FactoryBoy, what's the best way to fake an "updated" model field (that has either auto_add=True set on the model field or a .save() method with timezone.now), given that order of operations?

I've currently monkeypatched the .save() method on the original model before passing to FactoryBoy, is that the best way to do it?

[boxed]

@lmannering maybe the solution is to use freezegun and circumvent this and other problems all together?

[pymen]

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

[ashirazi2]

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

I know this is an old thread, but there is a third method that I use; override the date without saving…

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

foo = FooFactory.create()
foo.created_at = date(2001, 1, 1))
# use foo in assertion

[krystofbe]

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

I know this is an old thread, but there is a third method that I use; override the date without saving…

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

foo = FooFactory.create()
foo.created_at = date(2001, 1, 1))
# use foo in assertion

This was quite helpful. In addition to your approach, I found it necessary to include the .save() method to ensure the changes were persisted.