i need to group results by a field that requires a few joins from the original model:

// response_filter_args is created dynamically
responses = Response.objects.filter(**response_filter_args) \
        .values('customer__tags__tag') \                  # django doesn't like this
        .annotate(average_score=Avg('rating__score'))

Response -> customer -> tags (many-to-many field pointing to Tag) -> tag (the tag as a string)

Models are:

class Response(models.Model):
    customer = models.ForeignKey(Customer)
    ...

class Customer(models.Model):
    tags = models.ManyToManyField(Tag)
    ...

class Tag(models.Model):
    tag = models.CharField(max_length=255)
    ...

i'm trying to calculate average ratings. to make it work i need to tell django to group by 'tag', but it refuses to. it gives an error:

Invalid field name: 'customer__tags__tag'

anyone know how i can get it to group by tag? i've tried all the combinations of underscores in customer_tags_tag that i can think of, but nothing works.