generic relation generates needless join

[MS]

I have an generic relation, and tries to do some database queries with this relation.
When looking at the generated sql query i saw, that double joins are created. This happens
because generic relations are based on m2m table with a missing database table.

An example for the model:

from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic

class GenericTest(models.Model):
    contentType = models.ForeignKey(ContentType)
    objectId = models.PositiveIntegerField()
    contentObject = generic.GenericForeignKey('contentType', 'objectId')

class RefTest(models.Model):
    generic = generic.GenericRelation(GenericTest, content_type_field='contentType', object_id_field='objectId')
    testdata = models.PositiveIntegerField()

the query:

GenericTest.objects.filter(reftest__testdata=0)

as sql:

('SELECT U0.`id` FROM `test_generictest` U0 INNER JOIN `test_generictest` U1 ON (U0.`id` = U1.`id`) INNER JOIN `test_reftest` U2 ON (U1.`objectId` = U2.`id`) WHERE U2.`testdata` = %s ', (0,))

With the applied patch, which made the same test, which is done in the direct case, the sql query looks like:

('SELECT U0.`id` FROM `test_generictest` U0 INNER JOIN `test_reftest` U1 ON (U0.`id` = U1.`id`) WHERE U1.`testdata` = %s ', (0,))

For simple databases and simple sql queries, this extra join is no problem, but with complex ones, its a huge performance lack.

[Russell Keith-Magee]

This is possibly a regression caused by the recent m2m changes; needs further investigation.

[MS]

This bug is also in Django 1.1 so i think it's not a regression.

[MS]

The new patch has removed the double line, which was not nessecary in the patch before.

[Russell Keith-Magee]

Not critical for 1.2

[MS]

Patch für Double Joins

[MS]

There was another mistake in the patch, using the wrong database field with generic relations.

I am sad, that this patch won't be in 1.2, because it saves us a lot of time and ram used the database. Without it we would need a bigger server for database requests.

[Jacob]

Milestone 1.3 deleted

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Anssi Kääriäinen]

I am closing this as needsinfo. The query GenericTest.objects.filter(reftest__testdata=0) isn't valid Django query.