rails 中把关联的数据表单 直接变成 json对象 渲染

http://stackoverflow.com/questions/3462754/rails-object-relationships-and-json-rendering

主表：

class Pipeline < ActiveRecord::Base
    has_many  :sensors ,    :foreign_key => :pipeline_code ,:primary_key => :code
end

子表：

class Sensor < ActiveRecord::Base
    belongs_to :pipeline, :foreign_key => :pipeline_code ,:primary_key => :code
end

在conroler里面写 

 # 获取一个特定的桩孔和其属于的传感器信息
    def sensorsInThePipelineByCode()
        @pipeline = Pipeline.where(["code = ? ",params[:code]]).first;
        if respond_to do |format|
            format.html { render action: "show" }
            format.json {
                render json: @pipeline.to_json(:include => :sensors)
            }
          end
        end
    end

主要是：

@pipeline.to_json(:include => :sensors)

如果是多级关联 可以这么写 ：

 @pipeline_json.to_json(:include => {:sensors => {:include => :sensor_type }})