Admin interface does not check for incompatible generic relations

[Stefan Moluf]

# myapp.models.py
from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic

class User (models.Model):
    username = models.CharField(max_length=50, primary_key=True)
    birthdate = models.DateField()

class PhoneNumber:
    phone_number = PhoneNumberField()
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey()

# myapp.admin.py
from django.contrib import admin
from myapp.models import *
from django.contrib.contenttypes import generic

class PhoneNumberInline (admin.TabularInline):
    model = PhoneNumber

class UserAdmin (admin.ModelAdmin):
    inlines = [
        PhoneNumberInline,
    ]
admin.site.register(User, UserAdmin)

In the above example, a PhoneNumber cannot be associated with a User because the PhoneNumber stores object_id as a PositiveIntegerField, whereas the primary key of User is a CharField. However, the admin interface does not check for this and throws a ValueError exception when it attempts to give PhoneNumber.object_id (an integer) the value of User.username (a string).

It seems to me this should be a ConfigurationError.

[Ivan Giuliani]

This seems related to #8316.

[Ramiro Morales]

Ptahc that adds the validation for the reported user error and a couple of related ones

[Jacob]

It turns out that this is nearly impossible to check accurately. For example, the check in your patch for the class of the object_id field against the model's PK can't take into account fields that can be coerced into the right type. This is especially a problem because AutoField is one of those -- it's not an IntegerField, but it has a correctly typed value. Your check, then, prevents an IntegerField object_id from pointing to an AutoField, which is clearly incorrect. But it's more subtle than that: think about things like FilePathField that don't look anything like a CharField, but end up returning characters.

Ultimately, this is just a case where we have to expect users to do the right thing. We can't check every possible mistake someone might make.

[Jacob]

Milestone 1.1 deleted