Commit c28b7958 authored by Aymeric Augustin's avatar Aymeric Augustin
Browse files

Merge pull request #1164 from pyriku/get_or_create_through_m2m 

Integrity problems when using get_or_create through M2M
parents d34b1c29 65f9e0af

docs/ref/models/querysets.txt

+35 −0
Original line number Diff line number Diff line
@@ -1409,6 +1409,41 @@ has a side effect on your data. For more, see `Safe methods`_ in the HTTP spec. 


.. _Safe methods: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1



.. warning::



  You can use ``get_or_create()`` through :class:`~django.db.models.ManyToManyField`

  attributes and reverse relations. In that case you will restrict the queries

  inside the context of that relation. That could lead you to some integrity

  problems if you don't use it consistently.



  Being the following models::



      class Chapter(models.Model):

          title = models.CharField(max_length=255, unique=True)



      class Book(models.Model):

          title = models.CharField(max_length=256)

          chapters = models.ManyToManyField(Chapter)



  You can use ``get_or_create()`` through Book's chapters field, but it only

  fetches inside the context of that book::



      >>> book = Book.objects.create(title="Ulysses")

      >>> book.chapters.get_or_create(title="Telemachus")

      (<Chapter: Telemachus>, True)

      >>> book.chapters.get_or_create(title="Telemachus")

      (<Chapter: Telemachus>, False)

      >>> Chapter.objects.create(title="Chapter 1")

      <Chapter: Chapter 1>

      >>> book.chapters.get_or_create(title="Chapter 1")

      # Raises IntegrityError



  This is happening because it's trying to get or create "Chapter 1" through the

  book "Ulysses", but it can't do any of them: the relation can't fetch that

  chapter because it isn't related to that book, but it can't create it either

  because ``title`` field should be unique.





bulk_create

~~~~~~~~~~~

tests/get_or_create/models.py

+9 −0
Original line number Diff line number Diff line
@@ -28,3 +28,12 @@ class ManualPrimaryKeyTest(models.Model): 


class Profile(models.Model):

    person = models.ForeignKey(Person, primary_key=True)





class Tag(models.Model):

    text = models.CharField(max_length=256, unique=True)





class Thing(models.Model):

    name = models.CharField(max_length=256)

    tags = models.ManyToManyField(Tag)

tests/get_or_create/tests.py

+26 −1
Original line number Diff line number Diff line
@@ -6,7 +6,7 @@ import traceback 
from django.db import IntegrityError

from django.test import TestCase, TransactionTestCase



from .models import Person, ManualPrimaryKeyTest, Profile

from .models import Person, ManualPrimaryKeyTest, Profile, Tag, Thing





class GetOrCreateTests(TestCase):
@@ -77,3 +77,28 @@ class GetOrCreateTransactionTests(TransactionTestCase): 
            pass

        else:

            self.skipTest("This backend does not support integrity checks.")





class GetOrCreateThroughManyToMany(TestCase):



    def test_get_get_or_create(self):

        tag = Tag.objects.create(text='foo')

        a_thing = Thing.objects.create(name='a')

        a_thing.tags.add(tag)

        obj, created = a_thing.tags.get_or_create(text='foo')



        self.assertFalse(created)

        self.assertEqual(obj.pk, tag.pk)



    def test_create_get_or_create(self):

        a_thing = Thing.objects.create(name='a')

        obj, created = a_thing.tags.get_or_create(text='foo')



        self.assertTrue(created)

        self.assertEqual(obj.text, 'foo')

        self.assertIn(obj, a_thing.tags.all())



    def test_something(self):

        Tag.objects.create(text='foo')

        a_thing = Thing.objects.create(name='a')

        self.assertRaises(IntegrityError, a_thing.tags.get_or_create, text='foo')