ForeignKey should have a constraint

[Poromenos <poromenos@…>]

Most of the time when you have a ForeignKey you only want it to access some of the table's data, so I propose a constrained be implemented (like the one for the admin site). The constraint would be specified in the model and would be a QuerySet object that filters objects from the table and returns the suitable ones as FK choices.

This would also work in forms, limiting their choices.

[James Bennett]

Isn't this what limit_choices_to already does?

[Adrian Holovaty]

This is what limit_choices_to already does.

[Poromenos <poromenos@…>]

I will take another stab at this. limit_choices_to is not evaluated at call time, so it isn't exactly the same. I have modelA and modelB that have foreign keys to modelC. I want to be able to add a FK in modelA to modelB that will only display the objects in modelB that point to the same modelC as modelA (evaluated at call time).

[David Cramer]

That's something that would have to be done inside of Python, versus SQL. I think with newforms-admin being more seperated, this is something that should be pushed into there if its needed.

[Poromenos]

Would that work for newforms as well as the admin interface? The important part is the newforms one, because it would simplify almost every form that includes a foreign key (most django sites that include forms are multi-user setups, so the users should only see the FK choices of their own account, this is an example of where that would be useful).

[jkocherhans]

This is a duplicate of #2445.