adding a factory method to the join part for generating a table alias

activerecord/lib/active_record/associations/class_methods/join_dependency.rb

@@ -35,7 +35,7 @@ module ActiveRecord
 
         def columns
           join_parts.collect { |join_part|
-            table = Arel::Nodes::TableAlias.new join_part.aliased_table_name, nil
+            table = join_part.aliased_table
             join_part.column_names_with_alias.collect{ |column_name, aliased_name|
               table[column_name].as aliased_name
             }

activerecord/lib/active_record/associations/class_methods/join_dependency/join_part.rb

@@ -21,6 +21,10 @@ module ActiveRecord
             @cached_record = {}
           end
 
+          def aliased_table
+            Arel::Nodes::TableAlias.new aliased_table_name, table
+          end
+
           def ==(other)
             raise NotImplementedError
           end