CODEWITHSUNDEEP
djangodjango-models
Paul D. Waite
Paul D. Waite

Reputation: 98796

How can I filter objects from a Django model that are (ManyToMany) related to a specific set of objects in another model?

I’ve got a Django model (ModelA) with a ManyToManyField linking to another model (ModelB).

I’d like to write a query that selects all instances of Model A that are related to a specific set of instances from Model B.

I’d kind of like to do it like this:

related_set = ModelB.objects.filter(id__in=(1,2))
ModelA.objects.filter(modelb_set=related_set)

But that seems to select Model A instances that are related to instances 1 or 2 in Model B.

I want to select Model A instances that:

  1. are related to Model B instances 1 and 2;
  2. are not related to any other Model B instances.

Upvotes: 2

Views: 133

Answers (1)

Paul D. Waite
Paul D. Waite

Reputation: 98796

After some help from DrTyrsa, I think I’ve got it:

model_b_1 = ModelB.objects.get(id=1)
model_b_2 = ModelB.objects.get(id=2)
model_b_other = ModelB.objects.exclude(id__in(1, 2))

# Select Model A instances that are related to Model B instances 1 AND 2:
related_to_1_and_2 = ModelA.objects.filter(modelb=model_b_1).filter(modelb=model_b_2)

# Then exclude Model A instances that are related to any other Model B instances
ONLY_related_to_1_and_2 = related_to_1_and_2.exclude(modelb__in=model_b_other)

Upvotes: 1

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