Fixed #24215 -- Refactored lazy model operations

This adds a new method, Apps.lazy_model_operation(), and a helper function,
lazy_related_operation(), which together supersede add_lazy_relation() and
make lazy model operations the responsibility of the App registry. This
system no longer uses the class_prepared signal.

1 files changed, 38 insertions, 0 deletions

diff --git a/tests/apps/tests.py b/tests/apps/tests.py
index 89e295ffde..347996454f 100644
--- a/tests/apps/tests.py
+++ b/tests/apps/tests.py
@@ -259,6 +259,44 @@ class AppsTests(TestCase):
         finally:
             apps.apps_ready = True
 
+    def test_lazy_model_operation(self):
+        """
+        Tests apps.lazy_model_operation().
+        """
+        model_classes = []
+        initial_pending = set(apps._pending_operations)
+
+        def test_func(*models):
+            model_classes[:] = models
+
+        class LazyA(models.Model):
+            pass
+
+        # Test models appearing twice, and models appearing consecutively
+        model_keys = [('apps', model_name) for model_name in ['lazya', 'lazyb', 'lazyb', 'lazyc', 'lazya']]
+        apps.lazy_model_operation(test_func, *model_keys)
+
+        # LazyModelA shouldn't be waited on since it's already registered,
+        # and LazyModelC shouldn't be waited on until LazyModelB exists.
+        self.assertSetEqual(set(apps._pending_operations) - initial_pending, {('apps', 'lazyb')})
+
+        # Test that multiple operations can wait on the same model
+        apps.lazy_model_operation(test_func, ('apps', 'lazyb'))
+
+        class LazyB(models.Model):
+            pass
+
+        self.assertListEqual(model_classes, [LazyB])
+
+        # Now we are just waiting on LazyModelC.
+        self.assertSetEqual(set(apps._pending_operations) - initial_pending, {('apps', 'lazyc')})
+
+        class LazyC(models.Model):
+            pass
+
+        # Everything should be loaded - make sure the callback was executed properly.
+        self.assertListEqual(model_classes, [LazyA, LazyB, LazyB, LazyC, LazyA])
+
 
 class Stub(object):
     def __init__(self, **kwargs):