How to properly filter Many2Many / Generic Relations with Q?
I have 3 models, TaggedObject has GenericRelation with ObjectTagBridge. And ObjectTagBridge has a ForeignKey for 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 attach a tag to an object, I create a new ObjectTagBridge and set its ForeignKey tag to the tag I want to attach. This works fine and I can get all the tags that I have attached to the object very easily. But when I want to get (filter) all objects that have Tag1 and Tag2, I tried to do 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 two 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. Actually any combination of binary conjunctions like: (...) and ( (...) or not(...))
How can I filter this correctly? Each answer is appreciated, there may be another way to achieve this.
thanks for your help!!!
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If the result you are looking for is a TaggedObject with Tag1 and Tag2, consider a TaggedObject request instead of an ObjectTagBridge request. This is what this request looks like:
results = TaggedObject.objects.filter(objecttagbridge__tag = Tag1).filter(objecttagbridge__tag = Tag2)
Essentially, we are running two filters. Only objects with Tag1 and Tag2 will pass filter criteria and be part of the result set.
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It looks like you are trying to manually implement a Many-to-Many table and then join it with a generic relationship. A better approach might be to let Django handle M2M for you, and simply represent it in general terms like this:
class TaggedObject(models.Model):
"""
Help to connect a generic object to a Tag.
"""
content_type = models.ForeignKey(ContentType)
object_id = models.PositiveIntegerField()
content_object = generic.GenericForeignKey('content_type', 'object_id')
tags = models.ManyToManyField('Tag')
class Tag(models.Model):
...
This will allow you to do what you were trying to do ...
objects = TaggedObject.objects.filter( Q(tags=Tag1) & Q(tags=Tag2) )
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