How to filter Many2Many / Generic Relations properly with Q?

Posted by HWM-Rocker on Stack Overflow See other posts from Stack Overflow or by HWM-Rocker
Published on 2010-04-27T19:09:12Z Indexed on 2010/04/27 21:03 UTC
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Hi,

I have 3 Models, the TaggedObject has a GenericRelation with the ObjectTagBridge. And the ObjectTagBridge has a ForeignKey to the Tag Model.

class TaggedObject(models.Model):
    """
        class that represent a tagged object
    """
    tags = generic.GenericRelation('ObjectTagBridge',
                                   blank=True, null=True)

class ObjectTagBridge(models.Model):
    """
        Help to connect a generic object to a Tag.
    """
    # pylint: disable-msg=W0232,R0903
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')
    tag = models.ForeignKey('Tag')

class Tag(models.Model):
    ...

when I am attaching a Tag to an Object, I am creating a new ObjectTagBridge and set its ForeignKey tag to the Tag I want to attach. That is working fine, and I can get all Tags that I attached to my Object very easy. But when I want to get (filter) all Objects that have Tag1 and Tag2 I tried to something like this:

query = Q(tags__tag=Tag1) & Q(tags__tag=Tag2)
object_list = TaggedObjects.filter(query)

but now my object_list is empty, because it is looking for TaggedObjects that have one ObjectTagBridge with 2 tag objects, the first with Tag1 and the second with Tag2.

I my application will be more complex Q queries than this one, so I think I need a solution with this Q object. In fact any combination of binary conjunctions, like: (...) and ( (...) or not(...))

How can I filter this correctly? Every answer is welcome, maybe there is also a different way do achieve this.

thx for your help!!!

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