Lookup of attribute 'id' on model inheritance models in InlineModelAdmin fails when using fk_name of parent model

[Waldemar Hamm]

Having two models, of which one inherits from another, for example:

class Person(models.Model):
    firstname = models.CharField(max_length=255, blank=True)
    lastname = models.CharField(max_length=255)
    person_something = models.ForeignKey(Something)

class Author(Person):
    publisher = models.CharField(max_length=255)
    author_something = models.ForeignKey(Something)

I can't access the id field like so:

class AuthorInline(admin.StackedInline):
    model = Author
    fk_name = 'person_something'
    fields = ['id', 'lastname', 'publisher']
    readonly_fields = fields

class SomethingAdmin(admin.ModelAdmin):
    inlines = [ AuthorInline ]
    list_display = ('somethinga', 'somethingb')

I get a KeyError and it says:
"Key 'id' not found in 'AuthorForm'"

Using Author._meta.get_all_field_names() the field id is definitely in the model, though. Removing 'id' from the fields list makes everything work.

Am I doing something wrong or is this a legit bug?

[Tim Graham]

I think you need to use person_ptr in the fields list rather than id. I created a ​PR to add the list of possible fields to the KeyError message which would hopefully have helped you debug this. In this case, it adds "Choices are: DELETE, lastname, person_ptr, person_something, publisher."

[Tim Graham <timograham@…>]

In 3cb63b0:

Refs #26502 -- Added choices to Form.getitem() KeyError message.

[Waldemar Hamm]

Thanks a lot! :)

[Waldemar Hamm]

I tried using your suggestion but changing 'id' to 'person_ptr' in fields doesn't make the actual field appear within the admin object view.

It just resolved the error so the view appears at all. Why isn't the id/person_ptr field displayed?

[Tim Graham]

It's not an editable field as described in #11097. We might add some clarifying documentation as part of that ticket.

[Waldemar Hamm]

It's true that it is not visible in the example code I'm providing but actually I am using all of the provided fields as read_only fields. It's still not visible.

Is this also intended?

[Tim Graham]

Not sure, you should provide your actual code. That said, "is it a bug?" questions are better handled through our support channels.

[Waldemar Hamm]

I changed the Inline class to reflect what I'm talking about.
The person_ptr field is not displayed in the admin form as a readonly_field as well.

And even though it may not be a field that you are able to edit, using it as readonly_field and not being able to see it is, from my point of view, either a bug or doesn't follow the intuitive logic.

I asked if this was a bug, because I may not fully comprehend the full code logic behind Django, since I just started using it half a year ago. Now that I know that *_ptr is the field I am looking for and that the only limitation to it is not being editable I understand this situation as a bug.

[Tim Graham]

The issue is that the field uses a hidden widget by default so the HTML uses a ​"hidden" CSS class triggered by ​Fieldline.has_visible_field. You could likely change the widget in a custom admin form to workaround this.

It might make sense to try to allow readonly_fields to override override the widget automatically, but I'm not sure if a solution is feasible or if it might cause some other problems. In any case, let's open a separate ticket if you want to pursue such a solution since we've deviated quite a bit from the original report. Thanks.

[Waldemar Hamm]

Thank you for clarifying this, I wouldn't have found out about this so quick :).
I will try to create a custom admin form then and not pursue this any further for now. Thank you again, very much.