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rails中,你可以直接在对对象进行运算:
Task.sum(:priority)
Task.sum(:priority, :conditions => {:complete => false})
Task.minimum(:priority)
Task.maximum(:priority)
Task.average(:priority).to_f
Task.first.priority
这种做法有一个好处,就是不用把所有的对象返回然后用ruby来运算,大大降低的数据库的负载。
对于association,这种做法就更好了:
project.tasks.sum(:priority, :conditions=>{:complete => false})
内部执行sql如下:
SELECT sum("tasks".priority) AS sum_priority FROM "tasks" WHERE ("tasks"."completed" = 't') AND ("tasks".project_id = 1)
本文来自ChinaUnix博客,如果查看原文请点:http://blog.chinaunix.net/u/25407/showart_1918967.html |
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