由网友(滁ㄋωǒ 谁乜卟准疼伱)分享简介：我怎么能写一个AR查找查询已下令由记录中的has_many关联多少？How can I write an AR find query to have the results ordered by the number of records in a has_many association?class User <...

我怎么能写一个AR查找查询已下令由记录中的has_many关联多少？

How can I write an AR find query to have the results ordered by the number of records in a has_many association?

class User < ActiveRecord::Base
  has_many :photos
end

我想要做这样的事情......

I want to do something like...

User.find(:all, :order => photos.count)

我知道我的发现是无效的code。说我有以下数据。

I realize my find is not valid code. Say I have the following data.

User 1, which has 3 photos 
User 2, which has 5 photos 
User 3, which has 2 photos

我想我找到给我带回来的用户在......的顺序

I want my find to bring me back the users in the order of...

User 2, 
User 1, 
User 3

基于的用户的照片的计

based on the count of of the users photos

推荐答案

如果您不希望一个额外的列，你总是可以要求在返回的结果集一个额外的列：

If you don't want an extra column, you could always ask for an extra column in the returned result set:

User.all(:select => "#{User.table_name}.*, COUNT(#{Photo.table_name}.id) number_of_photos",
         :joins => :photos,
         :order => "number_of_photos")

这将生成的SQL语句：

This generates the following SQL:

SELECT users.*, COUNT(photos.id) number_of_photos
FROM `users` INNER JOIN `photos` ON photos.user_id = users.id
ORDER BY number_of_photos