Clarify that prepopulated_fields doesn't work with OneToOneField

[Malik A. Rumi]

I don't know if this should be a bug report or a feature request.

I know that some variation on this question has been asked and answered many times on Stack Overflow. Usually, however, it is about using a foreign key. This is not my question. "prepopulated_fields doesn’t accept DateTimeField, ForeignKey, nor ManyToManyField fields." ​https://docs.djangoproject.com/en/1.10/ref/contrib/admin/#django.contrib.admin.ModelAdmin.prepopulated_fields

By implication, the docs are saying OneToOne fields are ok. This makes even more sense where the inherited models are a concrete subclass of a concrete base and we are really talking about a single object. For example, a Place can be a Restaurant, and a Restaurant can have a closed off, separate Bar where kids are not allowed. ​https://docs.djangoproject.com/en/1.10/topics/db/models/#one-to-one-relationships

However, admin.py is looking for a string to concatenate, not a filtered queryset leading to a related field or object. Furthermore, it expects that string to match the name of an existing field on the instant model, not some other model, even if they are the same object. How, then, can one use a OneToOne field or model in admin.py? I posted this to SO myself, and got ZERO responses. ​http://stackoverflow.com/questions/39778945/django-prepopulated-fields-inheritance

Yes, I know about model-utils and polymorphic. But if I am reading the docs correctly, this should be possible without resort to those tools. Besides, both are aimed primarily at queries, and say nothing directly about this specific issue with prepopulated fields in admin.py. Please advise. Thanks.

[Tim Graham]

OneToOneField is a subclass of ForeignKey, so as far as I see, ​a system check error will occur. I guess the error message could be clarified since it confused you.

As far as getting answers to usage questions goes, please TicketClosingReasons/UseSupportChannels.

[Malik A. Rumi]

Replying to Tim Graham:

OneToOneField is a subclass of ForeignKey, so as far as I see, ​a system check error will occur. I guess the error message could be clarified since it confused you.

As far as getting answers to usage questions goes, please TicketClosingReasons/UseSupportChannels.

Ok. Thx.

[Sudheesh Singanamalla]

As far as what I understand from the discussion so far and the description, the fact that prepopulated_fields doesn't accept OneToOne fields needs to be explicitly mentioned in the documentation as well as an update to the following line ​https://github.com/django/django/blob/f734e2d4b2fc4391a4d097b80357724815c1d414/django/contrib/admin/checks.py#L402 mentioning

     else:
            if isinstance(field, (models.DateTimeField, models.ForeignKey, models.ManyToManyField)):
                return [
                    checks.Error(
                        "The value of '%s' refers to '%s', which must not be a DateTimeField, "
                        "a ForeignKey, a OneToOneField or a ManyToManyField." % (label, field_name),
                        obj=obj.__class__,
                        id='admin.E028',
                    )
                ]
            else:
                return []

Would this solve the issue ?

[Tim Graham]

Yes, please keep the comma before "or" in the message. A test could also be added.

[Malik A. Rumi]

Thanks guys. This will be a big help to all the literal minded people out there, like me.

[Henry Dang]

​PR

[Tim Graham <timograham@…>]

In 6af23a4:

Fixed #27377 -- Clarified that prepopulated_fields doesn't work with OneToOneField.

[Tim Graham <timograham@…>]

In 12c1d6f:

Refs #27377 -- Fixed reverse query name clash in test model.