raise an exception when p_id of orientdb user class will be duplicated

app/models/duplicated_user_index_error.rb

+class DuplicatedUserIndexError < Orientdb4r::ServerError
+end
\ No newline at end of file

app/repositories/orient_db/user_repository.rb

@@ -2,9 +2,15 @@ module OrientDb
   class UserRepository < Base
 
     def create_graph_node(user)
-      if user.persisted?
-        connection.command sprintf("create vertex User set p_id = %d", user.id)
-        return true
+      begin
+        if user.persisted?
+          connection.command sprintf("create vertex User set p_id = %d", user.id)
+          return true
+        end
+      rescue Orientdb4r::ServerError => e
+        if e.message =~ /ORecordDuplicatedException/
+          raise DuplicatedUserIndexError, 'The OrientDB index p_id of User class cannot be duplicated.'
+        end
       end
 
       raise NotPersistedRecordError, 'The user wasn`t persisted yet.'