Fixed #28987 -- Fixed altering ManyToManyField when changing to self-referential.

2 files changed, 68 insertions, 18 deletions

diff --git a/django/db/backends/sqlite3/schema.py b/django/db/backends/sqlite3/schema.py
index 88fa466f79..c9e924b182 100644
--- a/django/db/backends/sqlite3/schema.py
+++ b/django/db/backends/sqlite3/schema.py
@@ -174,7 +174,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             super().alter_field(model, old_field, new_field, strict=strict)
 
     def _remake_table(
-        self, model, create_field=None, delete_field=None, alter_field=None
+        self, model, create_field=None, delete_field=None, alter_fields=None
     ):
         """
         Shortcut to transform a model from old_model into new_model
@@ -213,15 +213,16 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         # If any of the new or altered fields is introducing a new PK,
         # remove the old one
         restore_pk_field = None
-        if getattr(create_field, "primary_key", False) or (
-            alter_field and getattr(alter_field[1], "primary_key", False)
+        alter_fields = alter_fields or []
+        if getattr(create_field, "primary_key", False) or any(
+            getattr(new_field, "primary_key", False) for _, new_field in alter_fields
         ):
             for name, field in list(body.items()):
-                if field.primary_key and not (
+                if field.primary_key and not any(
                     # Do not remove the old primary key when an altered field
                     # that introduces a primary key is the same field.
-                    alter_field
-                    and name == alter_field[1].name
+                    name == new_field.name
+                    for _, new_field in alter_fields
                 ):
                     field.primary_key = False
                     restore_pk_field = field
@@ -237,7 +238,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                     self.effective_default(create_field),
                 )
         # Add in any altered fields
-        if alter_field:
+        for alter_field in alter_fields:
             old_field, new_field = alter_field
             body.pop(old_field.name, None)
             mapping.pop(old_field.column, None)
@@ -457,7 +458,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                 )
             )
         # Alter by remaking table
-        self._remake_table(model, alter_field=(old_field, new_field))
+        self._remake_table(model, alter_fields=[(old_field, new_field)])
         # Rebuild tables with FKs pointing to this field.
         old_collation = old_db_params.get("collation")
         new_collation = new_db_params.get("collation")
@@ -495,18 +496,30 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             # propagate this altering.
             self._remake_table(
                 old_field.remote_field.through,
-                alter_field=(
-                    # The field that points to the target model is needed, so
-                    # we can tell alter_field to change it - this is
-                    # m2m_reverse_field_name() (as opposed to m2m_field_name(),
-                    # which points to our model).
-                    old_field.remote_field.through._meta.get_field(
-                        old_field.m2m_reverse_field_name()
+                alter_fields=[
+                    (
+                        # The field that points to the target model is needed,
+                        # so that table can be remade with the new m2m field -
+                        # this is m2m_reverse_field_name().
+                        old_field.remote_field.through._meta.get_field(
+                            old_field.m2m_reverse_field_name()
+                        ),
+                        new_field.remote_field.through._meta.get_field(
+                            new_field.m2m_reverse_field_name()
+                        ),
                     ),
-                    new_field.remote_field.through._meta.get_field(
-                        new_field.m2m_reverse_field_name()
+                    (
+                        # The field that points to the model itself is needed,
+                        # so that table can be remade with the new self field -
+                        # this is m2m_field_name().
+                        old_field.remote_field.through._meta.get_field(
+                            old_field.m2m_field_name()
+                        ),
+                        new_field.remote_field.through._meta.get_field(
+                            new_field.m2m_field_name()
+                        ),
                     ),
-                ),
+                ],
             )
             return
 
diff --git a/tests/migrations/test_operations.py b/tests/migrations/test_operations.py
index e02dc9ef3f..dc0d34eebd 100644
--- a/tests/migrations/test_operations.py
+++ b/tests/migrations/test_operations.py
@@ -1796,6 +1796,43 @@ class OperationTests(OperationTestBase):
         self.assertTableExists(original_m2m_table)
         self.assertTableNotExists(new_m2m_table)
 
+    def test_alter_model_table_m2m_field(self):
+        app_label = "test_talm2mfl"
+        project_state = self.set_up_test_model(app_label, second_model=True)
+        # Add the M2M field.
+        project_state = self.apply_operations(
+            app_label,
+            project_state,
+            operations=[
+                migrations.AddField(
+                    "Pony",
+                    "stables",
+                    models.ManyToManyField("Stable"),
+                )
+            ],
+        )
+        m2m_table = f"{app_label}_pony_stables"
+        self.assertColumnExists(m2m_table, "pony_id")
+        self.assertColumnExists(m2m_table, "stable_id")
+        # Point the M2M field to self.
+        with_field_state = project_state.clone()
+        operations = [
+            migrations.AlterField(
+                model_name="Pony",
+                name="stables",
+                field=models.ManyToManyField("self"),
+            )
+        ]
+        project_state = self.apply_operations(
+            app_label, project_state, operations=operations
+        )
+        self.assertColumnExists(m2m_table, "from_pony_id")
+        self.assertColumnExists(m2m_table, "to_pony_id")
+        # Reversal.
+        self.unapply_operations(app_label, with_field_state, operations=operations)
+        self.assertColumnExists(m2m_table, "pony_id")
+        self.assertColumnExists(m2m_table, "stable_id")
+
     def test_alter_field(self):
         """
         Tests the AlterField operation.