join_scopes

# File activerecord/lib/active_record/reflection.rb, line 1047
      def join_scopes(table, predicate_builder) # :nodoc:
        scopes = @previous_reflection.join_scopes(table, predicate_builder) + super
        if @previous_reflection.options[:source_type]
          scopes + [@previous_reflection.source_type_scope]
        else
          scopes
        end
      end