limit_choices_to won't limit correctly

[thanos@…]

If you set limit_choices_to, and then you hit the plus icon to add something to that list, that something will be one of your choices regardless of whether it confronts to the limit_choices_to restriction.

[Nuno Maltez <nuno@…>]

I can confirm this really happens: after you create a new object that does not fit the limit_choices_to restriction using the "plus icon", it will be selected in the form field, and listed in the dropdown.

However, saving will fail with the appropriate error message and the new object is removed from the dropdown.

I'm changing to "Design decision needed" because I'm not sure there's an easy fix and if this widget behaves likes this, well, "by design".

[Aymeric Augustin]

Looks like a bug.

[svisser]

Not as easy as it looks.

It happens because the response that response_add sends (in django.contrib.admin.options.ModelAdmin) unconditionally calls the JavaScript that updates the admin control. In practise the foreign key configuration may be complex so it may not be obvious to the user why the newly added object does not appear in the list. So it seems to me one would also need to inform the user about this.

Also, creating the new object happens by posting to the add_view and that view doesn't know what happens afterwards with that object. Solving this ticket would need a way of reevaluating the constraints in limit_choices_to but also elegantly communicate that to the front-end.

[svisser]

This seems similar to #20228; fixing one may also provide a stepping stone to fixing the other.