Add AlterIndexTogether operation

django/db/migrations/operations/__init__.py

@@ -1,2 +1,2 @@
-from .models import CreateModel, DeleteModel, AlterModelTable, AlterUniqueTogether
+from .models import CreateModel, DeleteModel, AlterModelTable, AlterUniqueTogether, AlterIndexTogether
 from .fields import AddField, RemoveField, AlterField, RenameField

django/db/migrations/operations/models.py

@@ -82,7 +82,7 @@ def describe(self):
 
 class AlterUniqueTogether(Operation):
     """
-    Changes the value of unique_together to the target one.
+    Changes the value of index_together to the target one.
     Input value of unique_together must be a set of tuples.
     """
 
@@ -108,3 +108,33 @@ def database_backwards(self, app_label, schema_editor, from_state, to_state):
 
     def describe(self):
         return "Alter unique_together for %s (%s constraints)" % (self.name, len(self.unique_together))
+
+
+class AlterIndexTogether(Operation):
+    """
+    Changes the value of index_together to the target one.
+    Input value of index_together must be a set of tuples.
+    """
+
+    def __init__(self, name, index_together):
+        self.name = name.lower()
+        self.index_together = set(tuple(cons) for cons in index_together)
+
+    def state_forwards(self, app_label, state):
+        model_state = state.models[app_label, self.name.lower()]
+        model_state.options["index_together"] = self.index_together
+
+    def database_forwards(self, app_label, schema_editor, from_state, to_state):
+        old_app_cache = from_state.render()
+        new_app_cache = to_state.render()
+        schema_editor.alter_index_together(
+            new_app_cache.get_model(app_label, self.name),
+            getattr(old_app_cache.get_model(app_label, self.name)._meta, "index_together", set()),
+            getattr(new_app_cache.get_model(app_label, self.name)._meta, "index_together", set()),
+        )
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        return self.database_forwards(app_label, schema_editor, from_state, to_state)
+
+    def describe(self):
+        return "Alter index_together for %s (%s constraints)" % (self.name, len(self.index_together))

tests/migrations/test_operations.py

@@ -30,6 +30,19 @@ def assertColumnNull(self, table, column):
     def assertColumnNotNull(self, table, column):
         self.assertEqual([c.null_ok for c in connection.introspection.get_table_description(connection.cursor(), table) if c.name == column][0], False)
 
+    def assertIndexExists(self, table, columns, value=True):
+        self.assertEqual(
+            value,
+            any(
+                c["index"]
+                for c in connection.introspection.get_constraints(connection.cursor(), table).values()
+                if c['columns'] == list(columns)
+            ),
+        )
+
+    def assertIndexNotExists(self, table, columns):
+        return self.assertIndexExists(table, columns, False)
+
     def set_up_test_model(self, app_label):
         """
         Creates a test model state and database table.
@@ -242,3 +255,25 @@ def test_alter_unique_together(self):
         cursor.execute("INSERT INTO test_alunto_pony (id, pink, weight) VALUES (1, 1, 1)")
         cursor.execute("INSERT INTO test_alunto_pony (id, pink, weight) VALUES (2, 1, 1)")
         cursor.execute("DELETE FROM test_alunto_pony")
+
+    def test_alter_index_together(self):
+        """
+        Tests the AlterIndexTogether operation.
+        """
+        project_state = self.set_up_test_model("test_alinto")
+        # Test the state alteration
+        operation = migrations.AlterIndexTogether("Pony", [("pink", "weight")])
+        new_state = project_state.clone()
+        operation.state_forwards("test_alinto", new_state)
+        self.assertEqual(len(project_state.models["test_alinto", "pony"].options.get("index_together", set())), 0)
+        self.assertEqual(len(new_state.models["test_alinto", "pony"].options.get("index_together", set())), 1)
+        # Make sure there's no matching index
+        self.assertIndexNotExists("test_alinto_pony", ["pink", "weight"])
+        # Test the database alteration
+        with connection.schema_editor() as editor:
+            operation.database_forwards("test_alinto", editor, project_state, new_state)
+        self.assertIndexExists("test_alinto_pony", ["pink", "weight"])
+        # And test reversal
+        with connection.schema_editor() as editor:
+            operation.database_backwards("test_alinto", editor, new_state, project_state)
+        self.assertIndexNotExists("test_alinto_pony", ["pink", "weight"])