[1.7.x] Fixed #23013 -- Fixed removing unique_together/index_together constraints in migrations.

Thanks melinath for the report.

Backport of 0154965392 from master

django/db/migrations/operations/models.py

@@ -248,7 +248,7 @@ class AlterUniqueTogether(Operation):
         return name.lower() == self.name.lower()
 
     def describe(self):
-        return "Alter %s for %s (%s constraint(s))" % (self.option_name, self.name, len(self.unique_together))
+        return "Alter %s for %s (%s constraint(s))" % (self.option_name, self.name, len(self.unique_together or ''))
 
 
 class AlterIndexTogether(Operation):
@@ -288,7 +288,7 @@ class AlterIndexTogether(Operation):
         return name.lower() == self.name.lower()
 
     def describe(self):
-        return "Alter %s for %s (%s constraint(s))" % (self.option_name, self.name, len(self.index_together))
+        return "Alter %s for %s (%s constraint(s))" % (self.option_name, self.name, len(self.index_together or ''))
 
 
 class AlterOrderWithRespectTo(Operation):

django/db/migrations/state.py

@@ -272,8 +272,6 @@ class ModelState(object):
         # First, make a Meta object
         meta_contents = {'app_label': self.app_label, "apps": apps}
         meta_contents.update(self.options)
-        if "unique_together" in meta_contents:
-            meta_contents["unique_together"] = list(meta_contents["unique_together"])
         meta = type(str("Meta"), tuple(), meta_contents)
         # Then, work out our bases
         try:

tests/migrations/test_operations.py

@@ -899,6 +899,10 @@ class OperationTests(OperationTestBase):
         operation.state_forwards("test_alunto", new_state)
         self.assertEqual(len(new_state.models["test_alunto", "pony"].options.get("unique_together", set())), 1)
 
+    def test_alter_unique_together_remove(self):
+        operation = migrations.AlterUniqueTogether("Pony", None)
+        self.assertEqual(operation.describe(), "Alter unique_together for Pony (0 constraint(s))")
+
     def test_alter_index_together(self):
         """
         Tests the AlterIndexTogether operation.
@@ -922,6 +926,10 @@ class OperationTests(OperationTestBase):
             operation.database_backwards("test_alinto", editor, new_state, project_state)
         self.assertIndexNotExists("test_alinto_pony", ["pink", "weight"])
 
+    def test_alter_index_together_remove(self):
+        operation = migrations.AlterIndexTogether("Pony", None)
+        self.assertEqual(operation.describe(), "Alter index_together for Pony (0 constraint(s))")
+
     def test_alter_model_options(self):
         """
         Tests the AlterModelOptions operation.