fix djangocms-versioning draft deletion bug (#214)

Previously, `djangocms_alias.models.AliasContent.delete` deleted all plugins
related to `AliasContent.alias`, with the same language. Drafts and previously
published versions included.
This meant that the deletion of a draft resulted in plugins disappearing from
published pages.

This patch removes the mechanism entirely and instead adds a warning, notifying
the user that the last version or translation of a language got deleted.

Signed-off-by: Florian Scherf <mail@florianscherf.de>

djangocms_alias/admin.py

@@ -2,7 +2,7 @@
 from cms.utils.permissions import get_model_permission_codename
 from cms.utils.urlutils import admin_reverse
 from django import forms
-from django.contrib import admin
+from django.contrib import admin, messages
 from django.http import (
     Http404,
     HttpRequest,
@@ -199,3 +199,13 @@ def has_module_permission(self, request: HttpRequest) -> bool:
         """Hides admin class in admin site overview"""
 
         return False
+
+    def delete_model(self, request: HttpRequest, obj: AliasContent):
+        if obj.alias._default_manager.filter(language=obj.language).count() == 1:
+            message = _("Alias content for language {} deleted. A new empty alias content will be created if needed.").format(obj.language)
+            self.message_user(request, message, level=messages.WARNING)
+
+        return super().delete_model(
+            request=request,
+            obj=obj,
+        )

djangocms_alias/models.py

@@ -316,11 +316,6 @@ def get_absolute_url(self):
     def get_template(self):
         return "djangocms_alias/alias_content.html"
 
-    @transaction.atomic
-    def delete(self, *args, **kwargs):
-        super().delete(*args, **kwargs)
-        self.alias.cms_plugins.filter(language=self.language).delete()
-
     @transaction.atomic
     def populate(self, replaced_placeholder=None, replaced_plugin=None, plugins=None):
         if not replaced_placeholder and not replaced_plugin: