join_scope

# File activerecord/lib/active_record/reflection.rb, line 191
      def join_scope(table)
        predicate_builder = predicate_builder(table)
        scope_chain_items = join_scopes(table, predicate_builder)
        klass_scope       = klass_join_scope(table, predicate_builder)

        scope_chain_items.inject(klass_scope || scope_chain_items.shift, &:merge!)
      end