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Fixes #18896. Add tests verifying that you can get IntegrityErrors us…

…ing get_or_create through relations like M2M, and it also adds a note into the documentation warning about it
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commit 65f9e0affd8ca04e2c597c43c1547ef7c888ec2a 1 parent d34b1c2
@pablorecio pablorecio authored
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35 docs/ref/models/querysets.txt
@@ -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
~~~~~~~~~~~
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9 tests/get_or_create/models.py
@@ -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)
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27 tests/get_or_create/tests.py
@@ -6,7 +6,7 @@
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 @@ def test_get_or_create_integrityerror(self):
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')
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