Fixed #22183: Through M2Ms now correctly handled

django/db/backends/schema.py

@@ -262,7 +262,8 @@ def create_model(self, model):
             })
         # Make M2M tables
         for field in model._meta.local_many_to_many:
-            self.create_model(field.rel.through)
+            if field.rel.through._meta.auto_created:
+                self.create_model(field.rel.through)
 
     def delete_model(self, model):
         """

django/db/models/fields/related.py

@@ -2032,6 +2032,11 @@ def deconstruct(self):
             kwargs['to'] = self.rel.to
         else:
             kwargs['to'] = "%s.%s" % (self.rel.to._meta.app_label, self.rel.to._meta.object_name)
+        if getattr(self.rel, 'through', None) is not None:
+            if isinstance(self.rel.through, six.string_types):
+                kwargs['through'] = self.rel.through
+            else:
+                kwargs['through'] = "%s.%s" % (self.rel.through._meta.app_label, self.rel.through._meta.object_name)
         # If swappable is True, then see if we're actually pointing to the target
         # of a swap.
         swappable_setting = self.swappable_setting

tests/field_deconstruction/tests.py

@@ -242,6 +242,12 @@ def test_many_to_many_field(self):
         self.assertEqual(args, [])
         self.assertEqual(kwargs, {"to": "auth.User"})
         self.assertEqual(kwargs['to'].setting_name, "AUTH_USER_MODEL")
+        # Test through
+        field = models.ManyToManyField("auth.Permission", through="auth.Group")
+        name, path, args, kwargs = field.deconstruct()
+        self.assertEqual(path, "django.db.models.ManyToManyField")
+        self.assertEqual(args, [])
+        self.assertEqual(kwargs, {"to": "auth.Permission", "through": "auth.Group"})
 
     @override_settings(AUTH_USER_MODEL="auth.Permission")
     def test_many_to_many_field_swapped(self):

tests/schema/models.py

@@ -44,6 +44,21 @@ class Meta:
         apps = new_apps
 
 
+class TagThrough(models.Model):
+    book = models.ForeignKey("schema.BookWithM2MThrough")
+    tag = models.ForeignKey("schema.TagM2MTest")
+
+    class Meta:
+        apps = new_apps
+
+
+class BookWithM2MThrough(models.Model):
+    tags = models.ManyToManyField("TagM2MTest", related_name="books", through=TagThrough)
+
+    class Meta:
+        apps = new_apps
+
+
 class BookWithSlug(models.Model):
     author = models.ForeignKey(Author)
     title = models.CharField(max_length=100, db_index=True)

tests/schema/tests.py

@@ -9,7 +9,7 @@
 from django.db.transaction import atomic
 from .models import (Author, AuthorWithM2M, Book, BookWithLongName,
     BookWithSlug, BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename,
-    UniqueTest, Thing)
+    UniqueTest, Thing, TagThrough, BookWithM2MThrough)
 
 
 class SchemaTests(TransactionTestCase):
@@ -26,7 +26,7 @@ class SchemaTests(TransactionTestCase):
     models = [
         Author, AuthorWithM2M, Book, BookWithLongName, BookWithSlug,
         BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename, UniqueTest,
-        Thing
+        Thing, TagThrough, BookWithM2MThrough
     ]
 
     # Utility functions
@@ -310,6 +310,20 @@ def test_m2m_create(self):
         columns = self.column_classes(BookWithM2M._meta.get_field_by_name("tags")[0].rel.through)
         self.assertEqual(columns['tagm2mtest_id'][0], "IntegerField")
 
+    def test_m2m_create_through(self):
+        """
+        Tests M2M fields on models during creation with through models
+        """
+        # Create the tables
+        with connection.schema_editor() as editor:
+            editor.create_model(TagThrough)
+            editor.create_model(TagM2MTest)
+            editor.create_model(BookWithM2MThrough)
+        # Ensure there is now an m2m table there
+        columns = self.column_classes(TagThrough)
+        self.assertEqual(columns['book_id'][0], "IntegerField")
+        self.assertEqual(columns['tag_id'][0], "IntegerField")
+
     def test_m2m(self):
         """
         Tests adding/removing M2M fields on models