Search code examples
djangoleft-joindjango-querysetdjango-select-related

A left outer reverse select_related in Django?

Imagine the following model:

class Parent(Model):
    ...

class Child(Model)
    father = ForeignKey(Parent)
    ...

Some parents have children, others do not (they're not parents in the real meaning, it's just a fictional name).

I would like to make the following query: I want to list all the Parents, and if they have children, bring me the children too. That would be the equivalent of a left outer join to Child table, that is:

select * from app_parent left join app_child on child_father_id=parent_id

This way, when I invoke Parent.child_set in my template, I won't hit the database a gazillion times. Is there a way to do that? Thanks

Solution

  • Starting from Django 1.4 prefetch_related does what you want.

    Parent.objects.prefetch_related('child_set')

    Related(!) django docs : https://docs.djangoproject.com/en/dev/ref/models/querysets/#prefetch-related.