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, 18 insertions, 0 deletions

diff --git a/django/db/models/utils.py b/django/db/models/utils.py
new file mode 100644
index 0000000000..f696e30ce2
--- /dev/null
+++ b/django/db/models/utils.py
@@ -0,0 +1,18 @@
+from django.utils import six
+
+
+def make_model_tuple(model):
+    """
+    Takes a model or a string of the form "app_label.ModelName" and returns a
+    corresponding ("app_label", "modelname") tuple. If a tuple is passed in,
+    it's assumed to be a valid model tuple already and returned unchanged.
+    """
+    if isinstance(model, tuple):
+        model_tuple = model
+    elif isinstance(model, six.string_types):
+        app_label, model_name = model.split(".")
+        model_tuple = app_label, model_name.lower()
+    else:
+        model_tuple = model._meta.app_label, model._meta.model_name
+    assert len(model_tuple) == 2, "Invalid model representation: %s" % model
+    return model_tuple