Django ModelChoiceField - use something other than id?

Question

Say I have an address table and it has a postal_code field -- ModelChoiceField does not allow me to use something other than PKs to validate existence

Answer 1

What about to_field_name? I'm not sure if it's documented anywhere, but you can find it easily between ModelChoiceField constructor params: https://github.com/django/django/blob/master/django/forms/models.py. It is used to filter field queryset.

For example:

articles = ModelChoiceField(queryset=Articles.objects.all(),
        to_field_name='slug')