Object creation fails if a ForeignKey field has an ID as default

[tobych]

I'm using f5784b, and I've a model with this field:

GENERIC_BUNNY_ID = 8
# ...
bunny_type = models.ForeignKey(BunnyType, default=GENERIC_BUNNY_ID)

When I try to instantiate this using G, I get:

File "/usr/local/lib/python2.6/dist-packages/django_dynamic_fixture-1.6.3-py2.6.egg/django_dynamic_fixture/ddf.py", line 370, in set_data_for_a_field
    setattr(instance, field.name, data) # Model.field = data
  File "/usr/local/lib/python2.6/dist-packages/django/db/models/fields/related.py", line 331, in __set__
    self.field.name, self.field.rel.to._meta.object_name))
ValueError: Cannot assign "8": "Asset.category" must be a "Category" instance.

I've not looked super long at the code, but I'll submit a pull request for code that's got it working for me.

Toby

[paulocheque]

Hi, thanks for reporting!

This patch sounds good for me. Do you create some automated test that reproduce this error to include in the pull request?

If you did not create, I will create for you.

Thanks again.

[tobych]

I didn't write a test actually. I think it was the day Github was down for a while and I couldn't do any work! Let me know if you'd still like me to do that.

[paulocheque]

Hi Toby.

I think with more attention about this. I believe this is an anti-pattern, since this will incentivate you to use a magic number in your models, and worst, a magic ID. Of course you can give a name to this constant, but I believe it is a better idea to create a method for this, so it will be possible to handle errors in a more properly way. Check the following example (I added an automated test for this scenario and it is working without any change in the code).

def default_fk_value():
    try:
        return ModelRelated.objects.get(id=1)
    except ModelRelated.DoesNotExist:
        return None

foreignkey_with_default = models.ForeignKey('ModelRelated', related_name='fk2', null=True, default=default_fk_value)

def test_new_deal_with_default_values(self):
    instance = self.ddf.new(ModelWithRelationships)
    self.assertTrue(isinstance(instance.foreignkey_with_default, ModelRelated))

What do you think? Do you agree?

Regards

[tobych]

Hi Paulo. I'm coming back to this rather late in the day, and only because of the subsequent issue you're referencing above. I do see what you're doing above, but my model is as I write, and I'm surprised you want to get involved in recommending certain approaches to modeling over others, I guess, and I know the foreign row will be there, so I don't need this extra code, and wouldn't like to have to change my model even this much to work around a limitation in DDF. Right now I'm using my fork of DDF.

[paulocheque]

I will include this patch in DDF!