find_join_association

# File activerecord/lib/active_record/associations/join_dependency.rb, line 135
      def find_join_association(name_or_reflection, parent)
        if String === name_or_reflection
          name_or_reflection = name_or_reflection.to_sym
        end

        join_associations.detect { |j|
          j.reflection == name_or_reflection && j.parent == parent
        }
      end