has_primary_key?

# File activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb, line 25
      def has_primary_key?
        return @has_primary_key unless @has_primary_key.nil?
        @has_primary_key = (@owner.connection.supports_primary_key? &&
          @owner.connection.primary_key(@reflection.options[:join_table]))
      end