A Mixin to prevent unnecessary queries in Django Formsets. This Mixin can be added to `admin.StackedInline` or `admin.TabularInline` in order to prevent querysets to be evaluated for each and every occurence of a `ModelChoiceField`. Say, you have a ModelAdmin that has currently 25 related objects in an InlineFormSet where each form has 2 Foreign…

fkey_choice_cache_mixin.py

 class ForeignKeyCacheMixin(object):
    """
    Cache foreignkey choices in the request object to prevent unnecessary queries.
    """
    def formfield_for_foreignkey(self, db_field, request, **kwargs):
        formfield = super(ForeignKeyCacheMixin, self).formfield_for_foreignkey(db_field, **kwargs)
        cache = getattr(request, 'db_field_cache', {})
        if cache.get(db_field.name):
            formfield.choices = cache[db_field.name]
        else:
            formfield.choices.field.cache_choices = True
            formfield.choices.field.choice_cache = [
                formfield.choices.choice(obj) for obj in formfield.choices.queryset.all()
            ]
            request.db_field_cache = cache
            request.db_field_cache[db_field.name] = formfield.choices
        return formfield

This works beautifully, thx!