GenericRelation fails to join the related table from a inherited model

[Ilya Semenov]

A minimalistic crashing example is worth thousands words:

class Car(models.Model):
        content_type = models.ForeignKey(ContentType)
        object_id = models.PositiveIntegerField()
        object = generic.GenericForeignKey()

class CarDriver(models.Model):
        cars = generic.GenericRelation(Car)

class Truck(Car):
        pass

class TruckDriver(models.Model):
        trucks = generic.GenericRelation(Truck)

# Selecting cars for a car drivers works fine

>>> john = CarDriver.objects.create()
>>> Car.objects.filter(cardriver=john)
[]

# Selecting trucks for a truck driver crashes

>>> pete = TruckDriver.objects.create()
>>> Truck.objects.filter(truckdriver=pete)
# OperationalError: (1054, "Unknown column 'T2.object_id' in 'where clause'")

[Ramiro Morales]

Can you exercise the same test case you've created against SVN trunk and report back the results please?

[Ilya Semenov]

The SQL query is a bit different in SVN trunk, but still results in the same error ("Unknown column 'T2.object_id' in 'where clause'").

SQL query in Django 1.1.1:

SELECT `tracker_car`.`id`, `tracker_car`.`content_type_id`, `tracker_car`.`object_id`, `tracker_truck`.`car_ptr_id`
FROM `tracker_truck`
INNER JOIN `tracker_truck` T2 ON (`tracker_truck`.`car_ptr_id` = T2.`id`)
INNER JOIN `tracker_car` ON (`tracker_truck`.`car_ptr_id` = `tracker_car`.`id`)
WHERE T2.`object_id` = 1 LIMIT 21

SQL query in Django-SVN r12453:

SELECT `tracker_car`.`id`, `tracker_car`.`content_type_id`, `tracker_car`.`object_id`, `tracker_truck`.`car_ptr_id`
FROM `tracker_truck`
INNER JOIN `tracker_truck` T2 ON (`tracker_truck`.`car_ptr_id` = T2.`car_ptr_id`)
INNER JOIN `tracker_car` ON (`tracker_truck`.`car_ptr_id` = `tracker_car`.`id`)
WHERE T2.`object_id` = 1 LIMIT 21

(By the way, I am also confused by the magic number 21, but that's irrelevant to the topic.)

[Ilya Semenov]

Just in case, the expected query is:

SELECT `tracker_car`.`id`, `tracker_car`.`content_type_id`, `tracker_car`.`object_id`, `tracker_truck`.`car_ptr_id`
FROM `tracker_truck`
INNER JOIN `tracker_car` ON (`tracker_truck`.`car_ptr_id` = `tracker_car`.`id`)
WHERE `tracker_car`.`object_id` = 1

• the redundant JOIN to itself removed along with its alias, and there's no "LIMIT 21".

I will probably look into the related ORM code on the weekend.

[Carl Meyer]

The magic "LIMIT 21" is added because the QuerySet is evaluated via repr. This is a safety feature to prevent careless use of "manage.py shell" from bringing your database to its knees.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Ramiro Morales]

See also #13203.

[Tim Graham]

This remains an issue as of 58c7ff39fb265754fb17ab8d7f8a1401b355777b (Django 1.10 dev).

Here's the query for the attached failing test:

SELECT "generic_relations_mineral"."id", "generic_relations_mineral"."name", "generic_relations_mineral"."hardness", "generic_relations_valuablerock"."mineral_ptr_id"
FROM "generic_relations_valuablerock"
INNER JOIN "generic_relations_valuabletaggeditem" ON ("generic_relations_valuablerock"."mineral_ptr_id" = "generic_relations_valuabletaggeditem"."object_id" AND ("generic_relations_valuabletaggeditem"."content_type_id" = 13)) 
INNER JOIN "generic_relations_taggeditem" ON ("generic_relations_valuabletaggeditem"."taggeditem_ptr_id" = "generic_relations_taggeditem"."id")
INNER JOIN "generic_relations_mineral" ON ("generic_relations_valuablerock"."mineral_ptr_id" = "generic_relations_mineral"."id")
WHERE "generic_relations_taggeditem"."tag" = countertop

Traceback:

File "/home/tim/code/django/django/db/backends/sqlite3/base.py", line 323, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.OperationalError: no such column: generic_relations_valuabletaggeditem.object_id

[Anssi Kääriäinen]

I've created a PR for this (see ​https://github.com/django/django/pull/5487). Luckily the changes needed here were only to contrib.contenttypes. This is always a good sign, we likely don't have a more fundamental problem. Lets see what CI things of my PR...

[Tim Graham <timograham@…>]

In cd0ba805:

Fixed #12885 -- Fixed queries with GenericRelations to multi-table inheritance child models.