#24997: Allow bulk_create with proxy inheritance
-------------------------------------+-------------------------------------
Reporter: wkschwartz | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.8
(models, ORM) | Keywords: proxy, inheritance,
Severity: Normal | bulk_create, queryset, insert
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
= Overview =
The [https://docs.djangoproject.com/en/1.8/ref/models/querysets/#bulk-
create documentation] for the Queryset method `bulk_create` states:
It does not work with child models in a multi-table inheritance scenario.
`bulk_create` also does not work with proxy inheritance, which does not
involve multiple tables. Rather than changing the documentation to reflect
that neither type of inheritance is supported, it would be better to allow
proxy inheritance to work.
= Origin of the problem =
It makes sense not to allow `bulk_create` with multiple tables. The
[https://github.com/django/django/blob/04e8d890aec8e996d568565555164a27a6a76057/django/db/models/query.py#L416
comment] in `bulk_create` explains it best:
So this case is fun. When you bulk insert you don't get the primary keys
back (if it's an autoincrement), so you can't insert into the child tables
which references this. There are two workarounds, 1) this could be
implemented if you didn't have an autoincrement pk, and 2) you could do it
by doing O(n) normal inserts into the parent tables to get the primary
keys back, and then doing a single bulk insert into the childmost table.
Some databases might allow doing this by using RETURNING clause for the
insert query. We're punting on these for now because they are relatively
rare cases.
`bulk_create` prevents inherited models from using it with
[https://github.com/django/django/blob/04e8d890aec8e996d568565555164a27a6a76057/django/db/models/query.py#L426
the following naive test]:
{{{#!python
if self.model._meta.parents:
raise ValueError("Can't bulk create an inherited model")
}}}
This test does not discriminate between multi-table inheritance and proxy
inheritance. However, simply modifying the code to read
{{{#!python
if self.model._meta.parents and not self.model._meta.proxy:
raise ValueError("Can't bulk create an inherited model with multiple
tables")
}}}
does not fix the problem because it results in more exceptions.
= Reproducing this error =
I did the following using Django 1.8.2 and Python 3.4.3 on Mac OS 10.9.5.
{{{#!bash
django-admin startproject bulk_create_proxy
cd bulk_create_proxy
./manage.py startapp app
}}}
Add `'app'` to the `INSTALLED_APPS` list in the resultant `settings.py`.
Save the following code in `app/models.py`.
{{{#!python
from django.db import models
class Parent(models.Model):
name = models.CharField(max_length=10)
class Child(Parent):
class Meta(object):
proxy = True
}}}
Save the following code in `app/tests.py`.
{{{#!python
from django.test import TestCase
from app.models import Parent, Child
class TestBulkCreate(TestCase):
def assert_can_bulk_create(self, model):
model.objects.all().delete()
model.objects.bulk_create([
model(name='a'), model(name='b'), model(name='c')])
self.assertEqual(model.objects.count(), 3)
def test_bulk_create_parent(self):
self.assert_can_bulk_create(Parent)
def test_bulk_create_child(self):
self.assert_can_bulk_create(Child)
}}}
Finish up with the following commands.
{{{#!bash
./manage.py makemigrations app
./manage.py migrate
./manage.py test
}}}
You should get the following test output. (I have elided file paths; ones
starting with `...django` come from Django.)
{{{
bulk_create_proxy ➜ ./manage.py test
Creating test database for alias 'default'...
E.
======================================================================
ERROR: test_bulk_create_child (app.tests.TestBulkCreate)
----------------------------------------------------------------------
Traceback (most recent call last):
File "...bulk_create_proxy/app/tests.py", line 18, in
test_bulk_create_child
self.assert_can_bulk_create(Child)
File "...bulk_create_proxy/app/tests.py", line 11, in
assert_can_bulk_create
model(name='a'), model(name='b'), model(name='c')])
File "...django/db/models/manager.py", line 127, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "...django/db/models/query.py", line 374, in bulk_create
raise ValueError("Can't bulk create an inherited model")
ValueError: Can't bulk create an inherited model
----------------------------------------------------------------------
Ran 2 tests in 0.003s
FAILED (errors=1)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/24997>
Django <https://code.djangoproject.com/>
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