trying to get pagent having children on django 1.6.

has_children_query.py

from django.db import models


class Parent(models.Model):
    name = models.CharField(max_length=255)

    def __str__(self):
        return self.name


class Child(models.Model):
    parent = models.ForeignKey(Parent)



#  Parent        Child
#
#  kaname  --+-- child
#            +-- child
#  saotome              (no children)
>>> from demoapp.models import Parent, Child
>>> saotome = Parent.objects.create(name='saotome')
>>> kaname = Parent.objects.create(name='kaname')
>>> Child.objects.create(parent=kaname)
>>> Child.objects.create(parent=kaname)
>>> 
>>> 
>>> Parent.objects.filter(child__isnull=True)
QUERY = 'SELECT "demoapp_parent"."id", "demoapp_parent"."name" FROM "demoapp_parent" LEFT OUTER JOIN "demoapp_child" ON ( "demoapp_parent"."id" = "demoapp_child"."parent_id" ) WHERE "demoapp_child"."id" IS NULL LIMIT 21' - PARAMS = () [0.17ms]
[<Parent: saotome>]
>>> Parent.objects.filter(child=None)
QUERY = 'SELECT "demoapp_parent"."id", "demoapp_parent"."name" FROM "demoapp_parent" LEFT OUTER JOIN "demoapp_child" ON ( "demoapp_parent"."id" = "demoapp_child"."parent_id" ) WHERE "demoapp_child"."id" IS NULL LIMIT 21' - PARAMS = () [0.10ms]
[<Parent: saotome>]
>>> Parent.objects.filter(child__isnull=False)
QUERY = 'SELECT "demoapp_parent"."id", "demoapp_parent"."name" FROM "demoapp_parent" INNER JOIN "demoapp_child" ON ( "demoapp_parent"."id" = "demoapp_child"."parent_id" ) WHERE "demoapp_child"."id" IS NOT NULL LIMIT 21' - PARAMS = () [0.15ms]
[<Parent: kaname>, <Parent: kaname>]
>>> Parent.objects.exclude(child=None)
QUERY = 'SELECT "demoapp_parent"."id", "demoapp_parent"."name" FROM "demoapp_parent" WHERE NOT ("demoapp_parent"."id" IN (SELECT U0."id" FROM "demoapp_parent" U0 LEFT OUTER JOIN "demoapp_child" U1 ON ( U0."id" = U1."parent_id" ) WHERE U1."id" IS NULL)) LIMIT 21' - PARAMS = () [0.20ms]
[<Parent: kaname>]
>>> Parent.objects.exclude(child__isnull=True)
QUERY = 'SELECT "demoapp_parent"."id", "demoapp_parent"."name" FROM "demoapp_parent" WHERE NOT ("demoapp_parent"."id" IN (SELECT U0."id" FROM "demoapp_parent" U0 LEFT OUTER JOIN "demoapp_child" U1 ON ( U0."id" = U1."parent_id" ) WHERE U1."id" IS NULL)) LIMIT 21' - PARAMS = () [0.14ms]
[<Parent: kaname>]
>>>

>>> Parent.objects.filter(child__isnull=False)

seems this line is strange a little

I found the corresponded ticket https://code.djangoproject.com/ticket/11347
It says use distinct() lol.