optimize generating link to fet meeting

fet2020/finance/admin.py

@@ -1,9 +1,11 @@
 import logging
 from datetime import date, datetime
+from urllib.parse import urljoin
 
-from django.conf import settings
 from django.contrib import admin, messages
+from django.contrib.sites.models import Site
 from django.http import HttpResponseRedirect
+from django.urls import reverse
 from django.utils.html import format_html
 from django.utils.translation import gettext_lazy as _
 from django.utils.translation import ngettext
@@ -473,7 +475,9 @@ class ResolutionAdmin(admin.ModelAdmin):
         fetmeeting = FetMeeting.objects.get_queryset().filter(date=obj.date).first()
 
         if fetmeeting is not None:
-            link = f"https://{settings.HOST_NAME}/posts/{fetmeeting.slug}/"
+            site = Site.objects.get_current()
+            path = reverse("show", kwargs={"id": fetmeeting.slug})
+            link = urljoin(f"https://{site.domain}", path)
             return format_html('<a href="{}" target="_blank">Link zur Fachschaftssitzung</a>', link)
 
         return format_html("-")