Fixed autoupdate for m2m relation. Fixed #4055.

CHANGELOG.rst

@@ -17,7 +17,7 @@ Core:
  - Enabled docs for using OpenSlides with Gunicorn and Uvicorn in big
    mode [#3799, #3817].
  - Changed format for elements send via autoupdate [#3926].
- - Fixed autoupdate system for related objects [#4140].
+ - Fixed autoupdate system for related objects [#4140, #4201].
  - Add a change-id system to get only new elements [#3938].
  - Switch from Yarn back to npm [#3964].
  - Added password reset link (password reset via email) [#3914, #4199].

openslides/core/apps.py

@@ -6,7 +6,7 @@ from typing import Any, Dict, List, Set
 
 from django.apps import AppConfig
 from django.conf import settings
-from django.db.models.signals import post_migrate
+from django.db.models.signals import post_migrate, pre_delete
 
 
 class CoreAppConfig(AppConfig):
@@ -20,6 +20,7 @@ class CoreAppConfig(AppConfig):
         from .projector import register_projector_slides
         from . import serializers  # noqa
         from .signals import (
+            autoupdate_for_many_to_many_relations,
             delete_django_app_permissions,
             get_permission_change_data,
             permission_change,
@@ -64,6 +65,10 @@ class CoreAppConfig(AppConfig):
             sender=self,
             dispatch_uid="core_save_config_default_values",
         )
+        pre_delete.connect(
+            autoupdate_for_many_to_many_relations,
+            dispatch_uid="core_autoupdate_for_many_to_many_relations",
+        )
 
         # Register viewsets.
         router.register(

openslides/core/signals.py

@@ -4,6 +4,8 @@ from django.contrib.contenttypes.models import ContentType
 from django.db.models import Q
 from django.dispatch import Signal
 
+from ..utils.autoupdate import Element, inform_changed_elements
+
 
 # This signal is send when the migrate command is done. That means it is sent
 # after post_migrate sending and creating all Permission objects. Don't use it
@@ -40,3 +42,32 @@ def get_permission_change_data(sender, permissions, **kwargs):
                 yield core_app.get_model("Countdown")
             elif permission.codename == "can_use_chat":
                 yield core_app.get_model("ChatMessage")
+
+
+def autoupdate_for_many_to_many_relations(sender, instance, **kwargs):
+    """
+    Send autoupdate for many-to-many related objects if the other side
+    is deleted.
+    """
+    m2m_fields = (
+        field
+        for field in instance._meta.get_fields(include_hidden=True)
+        if field.many_to_many and field.auto_created
+    )
+    for field in m2m_fields:
+        queryset = getattr(instance, field.get_accessor_name()).all()
+        for related_instance in queryset:
+            if hasattr(related_instance, "get_root_rest_element"):
+                # The related instance is or has a root rest element.
+                # So lets send it via autoupdate.
+                root_rest_element = related_instance.get_root_rest_element()
+                inform_changed_elements(
+                    [
+                        Element(
+                            collection_string=root_rest_element.get_collection_string(),
+                            id=root_rest_element.pk,
+                            full_data=None,
+                            reload=True,
+                        )
+                    ]
+                )