retrieve correct displaynames for users (from consumer if it is openHPI, otherwise use internal name)

app/models/external_user.rb

@@ -3,4 +3,13 @@ class ExternalUser < ActiveRecord::Base
 
   validates :consumer_id, presence: true
   validates :external_id, presence: true
+
+  def displayname
+    result = name
+    if(consumer.name == 'openHPI')
+      result = Xikolo::UserClient.get(external_id.to_s)[:display_name]
+    end
+    result
+  end
+
 end