ruby-on-rails-3 – 无法将HashWithIndifferentAccess转换为Stri

{"signed_request"=>"...","buyer"=>"1064897036","receiver"=>"1064897036","order_id"=>"224539980951036","method"=>"payments_get_items","test_mode"=>"1","order_info"=>{"description"=>"None","image_url"=>"","price"=>"1","product_url"=>"","title"=>"Premium Membership"}}

我正在借用一些代码来解析它并发回相应的响应.首先,我解析已签名的请求,该工作正常,然后我构建订单信息以将其发送回服务器.这就是麻烦开始的地方,似乎：

...
        elsif method == 'payments_get_items'

                  order_info = params[:order_info]

                  item = JSON.parse(order_info)
              item['price'] = item['price'].to_i

              # for url fields,if not prefixed by http://,prefix them
              url_key = [ 'product_url','image_url' ]
              url_key.each do |key|
                if item[key][0..6] != 'http://'
                  item[key] = "http://#{item[key]}"
                end
              end

 # if payload['test_mode']
              if request.params['test_mode']
                update_keys = ['title','description']
                update_keys.each do |key|
                    item[key] = '[Test Mode] ' + item[key]
                end
              end

              data['content'] = [item]  
            end

            data['method'] = method

            render :json => data
          end

我收到这个错误：

can't convert ActiveSupport::HashWithIndifferentAccess into String

这是由这条线引起的：

item = JSON.parse(order_info)

我不确定这意味着什么.替代方案,我想…是我可以让服务器传递一个项目号,然后我可以查询数据库并自己将信息作为JSON提取,而不是尝试解析哈希,但我想如果可以的话,让这项工作.有什么想法吗？