Could not find any way to limit_choices_to just the tags for a particular model

[GoogleCodeExporter]

So I wrote this one.

class LimitChoicesToTagsForModel(object):
    """
    For use with 'limit_choices_to' parameter in Foreign Relation model fields
    """
    def __init__(self, model):
        self.ctype_pk = ContentType.objects.get_for_model(model).pk

    def add_to_query(self, query, aliases):
        # Q objects are stupid complex, instead of duplicating their
behavior just use them directly
        query.add_q(models.Q(items__content_type__pk=self.ctype_pk))
        query.distinct = True

#Usage:
class Foo(models.Model):
  bar_by_tag = models.ManyToManyField(Tag,
limit_choices_to=LimitChoicesToTagsForModel(Bar))

FooAdmin(admin.ModelAdmin):
  filter_horizontal =('bar_by_tag',)

Then in admin interface you get nice selection widget with only valid tags
as choices

Original issue reported on code.google.com by njhar...@gmail.com on 31 Dec 2008 at 4:15