Can I make list_filter in django admin to only show referenced ForeignKeys?

Question

I have a django application which has two models like this:

class MyModel(models.Model):
    name = models.CharField()
    country = models.ForeignKey(\'Coun         


        

Answer 1

A generalized reusable version of the great @darklow's answer:

def make_RelatedOnlyFieldListFilter(attr_name, filter_title):

    class RelatedOnlyFieldListFilter(admin.SimpleListFilter):
        """Filter that shows only referenced options, i.e. options having at least a single object."""
        title = filter_title
        parameter_name = attr_name

        def lookups(self, request, model_admin):
            related_objects = set([getattr(obj, attr_name) for obj in model_admin.model.objects.all()])
            return [(related_obj.id, unicode(related_obj)) for related_obj in related_objects]

        def queryset(self, request, queryset):
            if self.value():
                return queryset.filter(**{'%s__id__exact' % attr_name: self.value()})
            else:
                return queryset

    return RelatedOnlyFieldListFilter

Usage:

class CityAdmin(ModelAdmin):
    list_filter = (
        make_RelatedOnlyFieldListFilter("country", "Country with cities"),
    )