rails中覆盖to_json方法的注意事项

最近一个项目中，使用到比较多的json，某个model因为一些原因，需要覆盖掉to_json，我简单的通过alias_method做了一个包装，代码如下：

    def to_json_with_ext
      "{\"data\":#{self.to_json_without_ext}}"
    end
    alias_method_chain :to_json, :ext

单元测试没有问题，但运行rails应用时，出现如下异常信息：

wrong number of arguments (1 for 0)

/usr/lib/ruby/gems/1.8/gems/activesupport-2.2.2/lib/active_support/json/encoding.rb:21:in `to_json'
/usr/lib/ruby/gems/1.8/gems/activesupport-2.2.2/lib/active_support/json/encoding.rb:21:in `send'
/usr/lib/ruby/gems/1.8/gems/activesupport-2.2.2/lib/active_support/json/encoding.rb:21:in `encode'
/usr/lib/ruby/gems/1.8/gems/activesupport-2.2.2/lib/active_support/json/encoding.rb:31:in `raise_on_circular_reference'
/usr/lib/ruby/gems/1.8/gems/activesupport-2.2.2/lib/active_support/json/encoding.rb:20:in `encode'
/usr/lib/ruby/gems/1.8/gems/activesupport-2.2.2/lib/active_support/json/encoders/enumerable.rb:10:in `to_json'
/usr/lib/ruby/gems/1.8/gems/activesupport-2.2.2/lib/active_support/json/encoders/enumerable.rb:10:in `map'

跟踪后发现，activerecord的to_json方法有一个参数options, to_json(options = {})，所以出现参数不匹配的异常，修改代码如下：

    def to_json_with_ext(options = {})
      "{\"data\":#{self.to_json_without_ext(options)}}"
    end
    alias_method_chain :to_json, :ext

运行通过。