选择列中具有最大列值的行

问题描述

我有一个表Person的ActiveRecord（：id，：name，：city_id，：work_id，：date）的数组。例如：

 可以使用rails的类方法。 
 
 
 
试试这个：
 
 
 Person.find_all_by_date（self.maximum（'date'））
 
 
 
查看一些详情 
 
I have an array of ActiveRecord of table Person (:id, :name, :city_id, :work_id, :date). For eg : 
[<Person id: 4, name: John, city_id: 10, work_id: 1, date: 2015-10-10>,
  <Person id: 5, name: Jack, city_id: 11, work_id: 2, date: 2015-10-08>,
  <Person id: 8, name: John, city_id: 10, work_id: 2, date: 2015-10-11>,
  <Person id: 9, name: John, city_id: 10, work_id: 3, date: 2015-10-11>,]
For a particular person, I want the rows with the maximum date. So, for Jack, I'll get row with id = 5. For John, I'll get the rows with id = [8,9] as the date is maximum for these rows. I can't figure out an efficient way to to this in Rails. Please help.
 解决方案 
You can use maximum class method of rails.
Try this:
Person.find_all_by_date(self.maximum('date'))
See some details here.
                        
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