source_reflection_name

# File activerecord/lib/active_record/reflection.rb, line 890
      def source_reflection_name # :nodoc:
        return @source_reflection_name if @source_reflection_name

        names = [name.to_s.singularize, name].collect(&:to_sym).uniq
        names = names.find_all { |n|
          through_reflection.klass._reflect_on_association(n)
        }

        if names.length > 1
          raise AmbiguousSourceReflectionForThroughAssociation.new(
            active_record.name,
            macro,
            name,
            options,
            source_reflection_names
          )
        end

        @source_reflection_name = names.first
      end