implement cache invalidation

leftists/apps.py

@@ -1,6 +1,13 @@
 from django.apps import AppConfig
+from django.db.models.signals import pre_save
 
 
 class LeftistsConfig(AppConfig):
     default_auto_field = 'django.db.models.BigAutoField'
     name = 'leftists'
+
+    def ready(self):
+        from . import signals
+        from .models import ShortLink
+
+        pre_save.connect(signals.rmcache, sender=ShortLink)

leftists/signals.py

@@ -0,0 +1,4 @@
+def rmcache(sender, **kwargs):
+    inst = kwargs.get("instance")
+    if inst.domain.fqdn in sender.cache:
+        del sender.cache[inst.domain.fqdn][inst.location]