[1.7.x] Fixed #24037 -- Prevented data loss possibility when changing Meta.managed.

The migrations autodetector now issues AlterModelOptions operations for
Meta.managed changes instead of DeleteModel + CreateModel.

Thanks iambibhas for the report and Simon and Markus for review.

Backport of 061caa5b386681dc7bdef16918873043224a299c from master

1 files changed, 19 insertions, 6 deletions

diff --git a/tests/migrations/test_autodetector.py b/tests/migrations/test_autodetector.py
index 38771f16ac..8beda8e552 100644
--- a/tests/migrations/test_autodetector.py
+++ b/tests/migrations/test_autodetector.py
@@ -1021,7 +1021,7 @@ class AutodetectorTests(TestCase):
         # The field name the FK on the book model points to
         self.assertEqual(changes['otherapp'][0].operations[0].fields[2][1].rel.field_name, 'pk_field')
 
-    def test_unmanaged(self):
+    def test_unmanaged_create(self):
         """Tests that the autodetector correctly deals with managed models."""
         # First, we test adding an unmanaged model
         before = self.make_project_state([self.author_empty])
@@ -1031,9 +1031,10 @@ class AutodetectorTests(TestCase):
         # Right number/type of migrations?
         self.assertNumberMigrations(changes, 'testapp', 1)
         self.assertOperationTypes(changes, 'testapp', 0, ["CreateModel"])
-        self.assertOperationAttributes(changes, 'testapp', 0, 0, name="AuthorUnmanaged")
-        self.assertEqual(changes['testapp'][0].operations[0].options['managed'], False)
+        self.assertOperationAttributes(changes, 'testapp', 0, 0,
+            name="AuthorUnmanaged", options={"managed": False})
 
+    def test_unmanaged_to_managed(self):
         # Now, we test turning an unmanaged model into a managed model
         before = self.make_project_state([self.author_empty, self.author_unmanaged])
         after = self.make_project_state([self.author_empty, self.author_unmanaged_managed])
@@ -1041,9 +1042,21 @@ class AutodetectorTests(TestCase):
         changes = autodetector._detect_changes()
         # Right number/type of migrations?
         self.assertNumberMigrations(changes, 'testapp', 1)
-        self.assertOperationTypes(changes, 'testapp', 0, ["DeleteModel", "CreateModel"])
-        self.assertOperationAttributes(changes, 'testapp', 0, 0, name="AuthorUnmanaged")
-        self.assertOperationAttributes(changes, 'testapp', 0, 1, name="AuthorUnmanaged")
+        self.assertOperationTypes(changes, 'testapp', 0, ["AlterModelOptions"])
+        self.assertOperationAttributes(changes, 'testapp', 0, 0,
+            name="authorunmanaged", options={})
+
+    def test_managed_to_unmanaged(self):
+        # Now, we turn managed to unmanaged.
+        before = self.make_project_state([self.author_empty, self.author_unmanaged_managed])
+        after = self.make_project_state([self.author_empty, self.author_unmanaged])
+        autodetector = MigrationAutodetector(before, after)
+        changes = autodetector._detect_changes()
+        # Right number/type of migrations?
+        self.assertNumberMigrations(changes, 'testapp', 1)
+        self.assertOperationTypes(changes, "testapp", 0, ["AlterModelOptions"])
+        self.assertOperationAttributes(changes, "testapp", 0, 0,
+            name="authorunmanaged", options={"managed": False})
 
     def test_unmanaged_custom_pk(self):
         """