diff --git a/app/models/application_model/has_cache.rb b/app/models/application_model/has_cache.rb
index 9a6f285dc..3da88c972 100644
--- a/app/models/application_model/has_cache.rb
+++ b/app/models/application_model/has_cache.rb
@@ -4,11 +4,7 @@ module ApplicationModel::HasCache
 
   included do
     before_create :cache_delete
-
-    after_create  :cache_delete
-    after_update  :cache_delete
-    after_touch   :cache_delete
-    after_destroy :cache_delete
+    after_commit :cache_delete
   end
 
   def cache_update(other)
diff --git a/app/models/observer/transaction.rb b/app/models/observer/transaction.rb
index 68c7cabf5..648e1ee7d 100644
--- a/app/models/observer/transaction.rb
+++ b/app/models/observer/transaction.rb
@@ -120,12 +120,12 @@ class Observer::Transaction < ActiveRecord::Observer
       # simulate article create as ticket update
       article = nil
       if event[:object] == 'Ticket::Article'
-        article = Ticket::Article.lookup(id: event[:id])
+        article = Ticket::Article.find_by(id: event[:id])
         next if !article
         next if event[:type] == 'update'
 
         # set new event infos
-        ticket = Ticket.lookup(id: article.ticket_id)
+        ticket = Ticket.find_by(id: article.ticket_id)
         event[:object] = 'Ticket'
         event[:id] = ticket.id
         event[:type] = 'update'
@@ -133,7 +133,7 @@ class Observer::Transaction < ActiveRecord::Observer
       end
 
       # get current state of objects
-      object = Kernel.const_get(event[:object]).lookup(id: event[:id])
+      object = Kernel.const_get(event[:object]).find_by(id: event[:id])
 
       # next if object is already deleted
       next if !object
diff --git a/app/models/ticket.rb b/app/models/ticket.rb
index a1f4777ef..49c1179a9 100644
--- a/app/models/ticket.rb
+++ b/app/models/ticket.rb
@@ -591,7 +591,7 @@ condition example
         elsif selector['pre_condition'] == 'current_user.organization_id'
           raise "Use current_user.id in selector, but no current_user is set #{selector.inspect}" if !current_user_id
           query += "#{attribute} IN (?)"
-          user = User.lookup(id: current_user_id)
+          user = User.find_by(id: current_user_id)
           bind_params.push user.organization_id
         else
           # rubocop:disable Style/IfInsideElse
@@ -624,7 +624,7 @@ condition example
           end
         elsif selector['pre_condition'] == 'current_user.organization_id'
           query += "#{attribute} NOT IN (?)"
-          user = User.lookup(id: current_user_id)
+          user = User.find_by(id: current_user_id)
           bind_params.push user.organization_id
         else
           # rubocop:disable Style/IfInsideElse
@@ -807,7 +807,7 @@ perform changes on ticket
     logger.debug { "Perform #{perform_origin} #{perform.inspect} on Ticket.find(#{id})" }
 
     article = begin
-                Ticket::Article.lookup(id: item.try(:dig, :article_id))
+                Ticket::Article.find_by(id: item.try(:dig, :article_id))
               rescue ArgumentError
                 nil
               end
@@ -847,18 +847,18 @@ perform changes on ticket
               elsif article.from.present?
                 recipients_raw.push(article.from)
               elsif article.origin_by_id
-                email = User.lookup(id: article.origin_by_id).email
+                email = User.find_by(id: article.origin_by_id).email
                 recipients_raw.push(email)
               elsif article.created_by_id
-                email = User.lookup(id: article.created_by_id).email
+                email = User.find_by(id: article.created_by_id).email
                 recipients_raw.push(email)
               end
             end
           elsif recipient == 'ticket_customer'
-            email = User.lookup(id: customer_id).email
+            email = User.find_by(id: customer_id).email
             recipients_raw.push(email)
           elsif recipient == 'ticket_owner'
-            email = User.lookup(id: owner_id).email
+            email = User.find_by(id: owner_id).email
             recipients_raw.push(email)
           elsif recipient == 'ticket_agents'
             User.group_access(group_id, 'full').sort_by(&:login).each do |user|
diff --git a/app/models/transaction/trigger.rb b/app/models/transaction/trigger.rb
index 0cda993b2..5faab763d 100644
--- a/app/models/transaction/trigger.rb
+++ b/app/models/transaction/trigger.rb
@@ -29,10 +29,10 @@ class Transaction::Trigger
 
     return if @item[:object] != 'Ticket'
 
-    ticket = Ticket.lookup(id: @item[:object_id])
+    ticket = Ticket.find_by(id: @item[:object_id])
     return if !ticket
     if @item[:article_id]
-      article = Ticket::Article.lookup(id: @item[:article_id])
+      article = Ticket::Article.find_by(id: @item[:article_id])
     end
 
     original_user_id = UserInfo.current_user_id
diff --git a/app/models/user_group.rb b/app/models/user_group.rb
index d7419c2da..b1d473764 100644
--- a/app/models/user_group.rb
+++ b/app/models/user_group.rb
@@ -19,7 +19,7 @@ class UserGroup < ApplicationModel
 
   def cache_delete
     group.cache_update(nil)
-    user.cache_update(nil)
+    user.cache_update(nil) if user.present?
     super
   end