Fixed #27666 -- Delayed rendering of recursivly related models in migration operations.

django/db/migrations/operations/fields.py

@@ -70,7 +70,9 @@ class AddField(FieldOperation):
         else:
             field = self.field
         state.models[app_label, self.model_name_lower].fields.append((self.name, field))
-        state.reload_model(app_label, self.model_name_lower)
+        # Delay rendering of relationships if it's not a relational field
+        delay = not field.is_relation
+        state.reload_model(app_label, self.model_name_lower, delay=delay)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         to_model = to_state.apps.get_model(app_label, self.model_name)
@@ -135,11 +137,16 @@ class RemoveField(FieldOperation):
 
     def state_forwards(self, app_label, state):
         new_fields = []
+        old_field = None
         for name, instance in state.models[app_label, self.model_name_lower].fields:
             if name != self.name:
                 new_fields.append((name, instance))
+            else:
+                old_field = instance
         state.models[app_label, self.model_name_lower].fields = new_fields
-        state.reload_model(app_label, self.model_name_lower)
+        # Delay rendering of relationships if it's not a relational field
+        delay = not old_field.is_relation
+        state.reload_model(app_label, self.model_name_lower, delay=delay)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         from_model = from_state.apps.get_model(app_label, self.model_name)
@@ -191,7 +198,11 @@ class AlterField(FieldOperation):
             for n, f in
             state.models[app_label, self.model_name_lower].fields
         ]
-        state.reload_model(app_label, self.model_name_lower)
+        # TODO: investigate if old relational fields must be reloaded or if it's
+        # sufficient if the new field is (#27737).
+        # Delay rendering of relationships if it's not a relational field
+        delay = not field.is_relation
+        state.reload_model(app_label, self.model_name_lower, delay=delay)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         to_model = to_state.apps.get_model(app_label, self.model_name)
@@ -270,7 +281,13 @@ class RenameField(FieldOperation):
                     [self.new_name if n == self.old_name else n for n in together]
                     for together in options[option]
                 ]
-        state.reload_model(app_label, self.model_name_lower)
+        for n, f in state.models[app_label, self.model_name_lower].fields:
+            if n == self.new_name:
+                field = f
+                break
+        # Delay rendering of relationships if it's not a relational field
+        delay = not field.is_relation
+        state.reload_model(app_label, self.model_name_lower, delay=delay)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         to_model = to_state.apps.get_model(app_label, self.model_name)

django/db/migrations/operations/models.py

@@ -331,10 +331,10 @@ class RenameModel(ModelOperation):
                     model_state.fields[index] = name, changed_field
                     model_changed = True
             if model_changed:
-                state.reload_model(model_app_label, model_name)
+                state.reload_model(model_app_label, model_name, delay=True)
         # Remove the old model.
         state.remove_model(app_label, self.old_name_lower)
-        state.reload_model(app_label, self.new_name_lower)
+        state.reload_model(app_label, self.new_name_lower, delay=True)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         new_model = to_state.apps.get_model(app_label, self.new_name)
@@ -444,7 +444,7 @@ class AlterModelTable(ModelOperation):
 
     def state_forwards(self, app_label, state):
         state.models[app_label, self.name_lower].options["db_table"] = self.table
-        state.reload_model(app_label, self.name_lower)
+        state.reload_model(app_label, self.name_lower, delay=True)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         new_model = to_state.apps.get_model(app_label, self.name)
@@ -521,7 +521,7 @@ class AlterUniqueTogether(FieldRelatedOptionOperation):
     def state_forwards(self, app_label, state):
         model_state = state.models[app_label, self.name_lower]
         model_state.options[self.option_name] = self.unique_together
-        state.reload_model(app_label, self.name_lower)
+        state.reload_model(app_label, self.name_lower, delay=True)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         new_model = to_state.apps.get_model(app_label, self.name)
@@ -575,7 +575,7 @@ class AlterIndexTogether(FieldRelatedOptionOperation):
     def state_forwards(self, app_label, state):
         model_state = state.models[app_label, self.name_lower]
         model_state.options[self.option_name] = self.index_together
-        state.reload_model(app_label, self.name_lower)
+        state.reload_model(app_label, self.name_lower, delay=True)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         new_model = to_state.apps.get_model(app_label, self.name)
@@ -626,7 +626,7 @@ class AlterOrderWithRespectTo(FieldRelatedOptionOperation):
     def state_forwards(self, app_label, state):
         model_state = state.models[app_label, self.name_lower]
         model_state.options['order_with_respect_to'] = self.order_with_respect_to
-        state.reload_model(app_label, self.name_lower)
+        state.reload_model(app_label, self.name_lower, delay=True)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         to_model = to_state.apps.get_model(app_label, self.name)
@@ -705,7 +705,7 @@ class AlterModelOptions(ModelOptionOperation):
         for key in self.ALTER_OPTION_KEYS:
             if key not in self.options and key in model_state.options:
                 del model_state.options[key]
-        state.reload_model(app_label, self.name_lower)
+        state.reload_model(app_label, self.name_lower, delay=True)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         pass
@@ -738,7 +738,7 @@ class AlterModelManagers(ModelOptionOperation):
     def state_forwards(self, app_label, state):
         model_state = state.models[app_label, self.name_lower]
         model_state.managers = list(self.managers)
-        state.reload_model(app_label, self.name_lower)
+        state.reload_model(app_label, self.name_lower, delay=True)
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
         pass

django/db/migrations/operations/special.py

@@ -181,6 +181,9 @@ class RunPython(Operation):
         pass
 
     def database_forwards(self, app_label, schema_editor, from_state, to_state):
+        # RunPython has access to all models. Ensure that all models are
+        # reloaded in case any are delayed.
+        from_state.clear_delayed_apps_cache()
         if router.allow_migrate(schema_editor.connection.alias, app_label, **self.hints):
             # We now execute the Python code in a context that contains a 'models'
             # object, representing the versioned models as an app registry.

django/db/migrations/state.py

@@ -52,6 +52,17 @@ def _get_related_models(m):
     return related_models
 
 
+def get_related_models_tuples(model):
+    """
+    Return a list of typical (app_label, model_name) tuples for all related
+    models for the given model.
+    """
+    return {
+        (rel_mod._meta.app_label, rel_mod._meta.model_name)
+        for rel_mod in _get_related_models(model)
+    }
+
+
 def get_related_models_recursive(model):
     """
     Return all models that have a direct or indirect relationship
@@ -85,6 +96,7 @@ class ProjectState(object):
         self.models = models or {}
         # Apps to include from main registry, usually unmigrated ones
         self.real_apps = real_apps or []
+        self.is_delayed = False
 
     def add_model(self, model_state):
         app_label, model_name = model_state.app_label, model_state.name_lower
@@ -100,7 +112,10 @@ class ProjectState(object):
             # the cache automatically (#24513)
             self.apps.clear_cache()
 
-    def reload_model(self, app_label, model_name):
+    def reload_model(self, app_label, model_name, delay=False):
+        if delay:
+            self.is_delayed = True
+
         if 'apps' in self.__dict__:  # hasattr would cache the property
             try:
                 old_model = self.apps.get_model(app_label, model_name)
@@ -109,7 +124,10 @@ class ProjectState(object):
             else:
                 # Get all relations to and from the old model before reloading,
                 # as _meta.apps may change
-                related_models = get_related_models_recursive(old_model)
+                if delay:
+                    related_models = get_related_models_tuples(old_model)
+                else:
+                    related_models = get_related_models_recursive(old_model)
 
             # Get all outgoing references from the model to be rendered
             model_state = self.models[(app_label, model_name)]
@@ -131,7 +149,10 @@ class ProjectState(object):
                 except LookupError:
                     pass
                 else:
-                    related_models.update(get_related_models_recursive(rel_model))
+                    if delay:
+                        related_models.update(get_related_models_tuples(rel_model))
+                    else:
+                        related_models.update(get_related_models_recursive(rel_model))
 
             # Include the model itself
             related_models.add((app_label, model_name))
@@ -169,8 +190,13 @@ class ProjectState(object):
         )
         if 'apps' in self.__dict__:
             new_state.apps = self.apps.clone()
+        new_state.is_delayed = self.is_delayed
         return new_state
 
+    def clear_delayed_apps_cache(self):
+        if self.is_delayed and 'apps' in self.__dict__:
+            del self.__dict__['apps']
+
     @cached_property
     def apps(self):
         return StateApps(self.real_apps, self.models)