CODEWITHSUNDEEP
djangodjango-queryset
Callum
Callum

Reputation: 1165

Django Query Relations Behaviour

Okay is there a way to filter the objects so that you only get records with associated records. Is it a right join maybe?

Basically, I only want to select records from A that B has a foreign key for whilst using a WHERE clause on B. Am i making it sound more complicated than it is? I don't need the records from B, just the A; maybe a subquery?

I'm relatively new to Django's queries and i've only just done some of the simpler stuff.

Upvotes: 0

Views: 49

Answers (2)

Callum
Callum

Reputation: 1165

My solution was a lot more simpler than I initially thought. I didn't know you could filter associated models so easily. Here's what I ended up with:

class A(models.Model):
    pass

class B(models.Model):
    a = models.ForeignKey(A)
    location = models.ForeignKey(Location)

a.filter(b__location=request.user.profile.location)

Upvotes: 0

Kevin Christopher Henry
Kevin Christopher Henry

Reputation: 48982

Your question is a little vague, but if I understand you correctly it would work like this:

class A(models.Model):
    pass

class B(models.Model):
    a = models.ForeignKey(A)
    some_field = models.IntegerField()

a.filter(b__some_field=5).distinct()

This JOINs the two tables and filters on b's some_field. Then distinct() makes sure that only unique as are returned. See the documentation on lookups that span relationships.

Upvotes: 1

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