Question

Situation

I have 3 models. Model A, model B and model C.

class A(Model):
    B_id = ForeignKey(B)
    id = IntegerField()
    pub_date = DateField()

class B(Model):
    id = IntegerField(primary_key = True)

class C(Model):
    B_id = ForeignKey(B)
    pub_date = DateField()
    information = TextField()

Model A and model C both have a field called B_id, which is a foreign key to model B. So there is no direct connection from B to A or C.

Goal

I’m given an ID from model A. Now I need all informations from C where the pub_date matches the pub_date in A and the B_id matches the B_id in A.

In SQL, this would be a pretty easy query:

SELECT C.information FROM A JOIN C USING(B_id, pub_date) WHERE A.id = 1234;

But I simply can’t figure out how to do this in Django ORM syntax, as a filter()-clause only works if there is a direct connection path from C to A.

—

Edit: Please note that there is more than one row in A that matches one id.

Answer 1

EDIT:

Try this:

 A.objects.filter(B_id__c__pub_date=F('pub_date'))

I’m not 100% sure about the capitalization on the filter string, but the F() predicate is what you are looking for. See the docs.