Allow propagation of ignored_fields to automatically generated Foreign Key

[k4rl85]

Hi, i have some problem with the integration between django-polymorphic and django-dynamic-fixtures.

This was talked in different issues and some fix has been done like #85. The problem for me is the automatic generation of a foreign key releated to a polymorphic instance.

The solution suggested in #85 is to set DDF_IGNORE_FIELDS = ['*_ptr'] but this solution is ineffective in my case, because the DDF code does not use ignored_fields with an auto generated related object.

Example:

# settings.py
DDF_IGNORE_FIELDS = ['*_ptr']

# models.py
class Location(PolymorphicModel):
    objects = PolymorphicManager()

class Country(Location):
    name = models.CharField(max_length=200)

class Publisher(models.Model):
    country = models.ForeignKey(Country, null=True, blank=True)

# test.py
from django_dynamic_fixture import G

G(Country)  # <-- no problem
G(Publisher)  # <-- raise Attribution error

The error generated in 2nd call is caused by the implicit creation of a Country for the Publisher instance. The ignored fields are not correctly set for the publisher country because it receive an empty ignored_fields.

I wonder if there is a reason to avoid this propagation, i will prepare a PR to fix it if is not needed.

Carlo

[paulocheque]

Hi there, first of all, thanks for the report and for the PR.

The reason to avoid this propagation is because two models can have fields with the same name.

class ModelA:
    name = charfield

class ModelB:
    name = charfield
    a = FK(A)

G(ModelA, ignore_fields=['name']) # should ignore just name in ModelA.

Do you think it is possible to adjust the PR to support both situations?

Maybe you could create a new option like ignore_all_fields or something?

Or maybe we can add some prefix to tell DDF to propagate, like ignore_fields=['*name'].

What do you think?

[k4rl85]

I would stay with the current G(ModelA, ignore_fields=[...]) behavior, i.e. explicit ignore_fields will be applied only to ModelA and NOT to related objects (ModelB), created together with the A instance. While ignore fields declared in settings should be applied to A and B, being them intended to be applied globally.

I will modify the PR to show my solution

[paulocheque]

Thanks again.

But I did not understand the new PR completely. What is the difference of behavior with and without the PR https://github.com/paulocheque/django-dynamic-fixture/pull/90?

[k4rl85]

I have dug a lot to find a solution so prepare for a very long message :D

The codebase have 3 point where a DynamicFixture object are initialized:

• in __init__.py fixture function
• in DynamicFixture._process_foreign_key method
• in DynamicFixture._create_manytomany_relationship method

the problem without the PR is that only in the first case use the DDF_IGNORE_FIELDS setting so with my PR i ensure that any call of DynamicFixture() will use the generic ignore_fields.

BTW the solution proposed in #85 is wrong because by ignoring *_ptr it does not return error on G() call but the created obj is not valid! When you try to retrieve from db the new obj it will fail. https://docs.djangoproject.com/en/1.11/topics/db/models/#multi-table-inheritance

# settings
DDF_IGNORE_FIELDS = ['*_ptr']

# model.py
class ModelA(PolymorphicModel):
    ...

class ModelB(ModelA):
    ...

class ModelC(models.Model):
    a = FK(ModelB)

# test.py
obj = G(ModelB)
ModelB.objects.get(pk=obj.pk) # <-- Here django throw error because he cannot find a valid parent instance of ModelA relative the created obj

The real solution to fix the integration with django-polymorphic is to avoid creation of polymorphic_ctype field with this code:

DDF_IGNORE_FIELDS = ['polymorphic_ctype']

and modify set_data_for_a_field method to handle an AttributeError raised by *_ptr fields.

I don't know why multi table inheritance does not raise an AttributeError while django-polymorphic does it.

[paulocheque]

What amazing explanation and contribution! =)

I merged the PR.

Thanks!