Checks for ModelAdmin ForeignKeys fail with GenericInlineModelAdmin

[Julian Wachholz]

Checks admin.E202 fail when trying to detect a ForeignKey from a GenericInlineModelAdmin:

The following setup yields this error:

<class 'app.admin.BarInline'>: (admin.E202) 'app.Bar' has no ForeignKey to 'app.Foo'.

models.py

class Foo(models.Model):
    """Foo may have some Bars."""
    text = models.TextField()

class Bar(models.Model):
    text = models.TextField()

    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')

admin.py

class BarInline(GenericStackedInline):
    model = Bar

@admin.register(Foo)
class FooAdmin(admin.ModelAdmin):
    inlines = [BarInline]

I think this will require an exception in _check_fk_name for generic InlineAdmin classes here:
​https://github.com/django/django/blob/06bd181f97e5e5561ae7e80efae4c38ee670773f/django/contrib/admin/checks.py#L866

[Marco Badan]

I've 3 errors:

<class 'app.admin.BarInline'>: (admin.E202) 'app.Bar' has no ForeignKey to 'app.Foo'.
Bar.content_object: (contenttypes.E001) The field refers to "Bar.object_id" field which is missing.
Bar.content_object: (contenttypes.E005) The field refers to Bar.content_type field which is missing.

But object_id and content_type fields are in my database.

Note for @jwa: contenttypes.generic has been deprecated (​https://github.com/django/django/commit/10e3faf191d8f230dde8534d1c8fad8c8717816e)

[Russell Keith-Magee]

This is a newly added system check, so it's a release blocker.

[josven]

These is a PR: ​https://github.com/django/django/pull/2351
I'm introducing dependency to django.contrib.contenttypes.fields.GenericForeignKey.
Don't know if this is acceptable or not.

[josven]

Changed the approach.

• Created a GenericInlineModelAdminChecks that override def _check_fk_name.
• Moved the dependency for django.contrib.contenttypes in django.conrtib.admin.checks, to having a dependency for django.contrib.admin.checks in django.contrib.contenttypes.checks instead.

​https://github.com/django/django/pull/2351

[josven]

The lastest approach did not completely work. The previous commit ​https://github.com/josven/django/commit/b697147d0b9e4b762aae7b2c057231894d6098c2 still works.

[Collin Anderson]

I can confirm that the current pull request doesn't fix it but ​​https://github.com/josven/django/commit/b697147 works for me.

As far as the dependency goes, could we have a Inline._check_fk() on all inlines that lazy-imports code to handle the check?

Or, have a hook like Inline._checks = 'django.contrib.contenttypes.checks.GenericInlineModelAdminChecks'

As a side note, I like to do hacky things with my inlines (like store data in json on the original model) and sometimes that means it doesn't make sense to have an actual foreign key.

[Russell Keith-Magee]

The problem here is that GenericInlineModelAdmin is using the base InlineModelAdmin checks. We just need to make GenericInlineModelAdmin run it's own, generic-specific checks of the relation to the parent.

I'm working on a patch, incoming shortly.

[Russell Keith-Magee <russell@…>]

In 70ec4d776ef0e68960ccee21476b8654e9399f53:

Fixed #22034 -- Added a specific set of relation checks for GenericInlineModelAdmin.

Thanks to jwa for the report.