[1.10.x] Fixed #25044 -- Fixed migrations for renaming ManyToManyField's through model.

Backport of f1e408ff40 from master

AUTHORS

@@ -758,6 +758,7 @@ answer newbie questions, and generally made Django that much better:
     Vladimir Kuzma <vladimirkuzma.ch@gmail.com>
     Vlado <vlado@labath.org>
     Vsevolod Solovyov
+    Vytis Banaitis <vytis.banaitis@gmail.com>
     wam-djangobug@wamber.net
     Wang Chun <wangchun@exoweb.net>
     Warren Smith <warren@wandrsmith.net>

django/db/migrations/autodetector.py

@@ -867,6 +867,13 @@ class MigrationAutodetector(object):
                 )
                 if rename_key in self.renamed_models:
                     new_field.remote_field.model = old_field.remote_field.model
+            if hasattr(new_field, "remote_field") and getattr(new_field.remote_field, "through", None):
+                rename_key = (
+                    new_field.remote_field.through._meta.app_label,
+                    new_field.remote_field.through._meta.model_name,
+                )
+                if rename_key in self.renamed_models:
+                    new_field.remote_field.through = old_field.remote_field.through
             old_field_dec = self.deep_deconstruct(old_field)
             new_field_dec = self.deep_deconstruct(new_field)
             if old_field_dec != new_field_dec:

django/db/migrations/operations/models.py

@@ -307,6 +307,28 @@ class RenameModel(ModelOperation):
                 new_fields.append((name, field))
             state.models[related_key].fields = new_fields
             state.reload_model(*related_key)
+        # Repoint M2Ms with through pointing to us
+        related_models = {
+            f.remote_field.model for f in model._meta.fields
+            if getattr(f.remote_field, 'model', None)
+        }
+        model_name = '%s.%s' % (app_label, self.old_name)
+        for related_model in related_models:
+            if related_model == model:
+                related_key = (app_label, self.new_name_lower)
+            else:
+                related_key = (related_model._meta.app_label, related_model._meta.model_name)
+            new_fields = []
+            changed = False
+            for name, field in state.models[related_key].fields:
+                if field.is_relation and field.many_to_many and field.remote_field.through == model_name:
+                    field = field.clone()
+                    field.remote_field.through = '%s.%s' % (app_label, self.new_name)
+                    changed = True
+                new_fields.append((name, field))
+            if changed:
+                state.models[related_key].fields = new_fields
+                state.reload_model(*related_key)
         state.reload_model(app_label, self.new_name_lower)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):

tests/migrations/test_autodetector.py

@@ -259,6 +259,10 @@ class AutodetectorTests(TestCase):
         ("id", models.AutoField(primary_key=True)),
         ("publishers", models.ManyToManyField("testapp.Publisher", through="testapp.Contract")),
     ])
+    author_with_renamed_m2m_through = ModelState("testapp", "Author", [
+        ("id", models.AutoField(primary_key=True)),
+        ("publishers", models.ManyToManyField("testapp.Publisher", through="testapp.Deal")),
+    ])
     author_with_former_m2m = ModelState("testapp", "Author", [
         ("id", models.AutoField(primary_key=True)),
         ("publishers", models.CharField(max_length=100)),
@@ -286,6 +290,11 @@ class AutodetectorTests(TestCase):
         ("author", models.ForeignKey("testapp.Author", models.CASCADE)),
         ("publisher", models.ForeignKey("testapp.Publisher", models.CASCADE)),
     ])
+    contract_renamed = ModelState("testapp", "Deal", [
+        ("id", models.AutoField(primary_key=True)),
+        ("author", models.ForeignKey("testapp.Author", models.CASCADE)),
+        ("publisher", models.ForeignKey("testapp.Publisher", models.CASCADE)),
+    ])
     publisher = ModelState("testapp", "Publisher", [
         ("id", models.AutoField(primary_key=True)),
         ("name", models.CharField(max_length=100)),
@@ -848,6 +857,21 @@ class AutodetectorTests(TestCase):
         # no AlterField for the related field.
         self.assertNumberMigrations(changes, 'otherapp', 0)
 
+    def test_rename_m2m_through_model(self):
+        """
+        Tests autodetection of renamed models that are used in M2M relations as
+        through models.
+        """
+        # Make state
+        before = self.make_project_state([self.author_with_m2m_through, self.publisher, self.contract])
+        after = self.make_project_state([self.author_with_renamed_m2m_through, self.publisher, self.contract_renamed])
+        autodetector = MigrationAutodetector(before, after, MigrationQuestioner({'ask_rename_model': True}))
+        changes = autodetector._detect_changes()
+        # Right number/type of migrations?
+        self.assertNumberMigrations(changes, 'testapp', 1)
+        self.assertOperationTypes(changes, 'testapp', 0, ['RenameModel'])
+        self.assertOperationAttributes(changes, 'testapp', 0, 0, old_name='Contract', new_name='Deal')
+
     def test_rename_model_with_renamed_rel_field(self):
         """
         Tests autodetection of renamed models while simultaneously renaming one

tests/migrations/test_operations.py

@@ -727,6 +727,47 @@ class OperationTests(OperationTestBase):
         self.assertEqual(Rider.objects.count(), 2)
         self.assertEqual(Pony._meta.get_field('riders').remote_field.through.objects.count(), 2)
 
+    def test_rename_m2m_through_model(self):
+        app_label = "test_rename_through"
+        project_state = self.apply_operations(app_label, ProjectState(), operations=[
+            migrations.CreateModel("Rider", fields=[
+                ("id", models.AutoField(primary_key=True)),
+            ]),
+            migrations.CreateModel("Pony", fields=[
+                ("id", models.AutoField(primary_key=True)),
+            ]),
+            migrations.CreateModel("PonyRider", fields=[
+                ("id", models.AutoField(primary_key=True)),
+                ("rider", models.ForeignKey("test_rename_through.Rider", models.CASCADE)),
+                ("pony", models.ForeignKey("test_rename_through.Pony", models.CASCADE)),
+            ]),
+            migrations.AddField(
+                "Pony",
+                "riders",
+                models.ManyToManyField("test_rename_through.Rider", through="test_rename_through.PonyRider"),
+            ),
+        ])
+        Pony = project_state.apps.get_model(app_label, "Pony")
+        Rider = project_state.apps.get_model(app_label, "Rider")
+        PonyRider = project_state.apps.get_model(app_label, "PonyRider")
+        pony = Pony.objects.create()
+        rider = Rider.objects.create()
+        PonyRider.objects.create(pony=pony, rider=rider)
+
+        project_state = self.apply_operations(app_label, project_state, operations=[
+            migrations.RenameModel("PonyRider", "PonyRider2"),
+        ])
+        Pony = project_state.apps.get_model(app_label, "Pony")
+        Rider = project_state.apps.get_model(app_label, "Rider")
+        PonyRider = project_state.apps.get_model(app_label, "PonyRider2")
+        pony = Pony.objects.first()
+        rider = Rider.objects.create()
+        PonyRider.objects.create(pony=pony, rider=rider)
+        self.assertEqual(Pony.objects.count(), 1)
+        self.assertEqual(Rider.objects.count(), 2)
+        self.assertEqual(PonyRider.objects.count(), 2)
+        self.assertEqual(pony.riders.count(), 2)
+
     def test_add_field(self):
         """
         Tests the AddField operation.