如何按 has_many 关系中的对象数量对 Rails AR.find 进行排序 [英] How to sort Rails AR.find by number of objects in a has_many relationship

问题描述

如何编写 AR 查找查询以按 has_many 关联中的记录数对结果进行排序?

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

我想做类似...

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

我意识到我的发现不是有效代码.假设我有以下数据.

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 

我希望我的发现按...的顺序将我带回用户

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

User 2, 
User 1, 
User 3 

基于用户照片的数量

推荐答案

如果你不想要额外的列，你总是可以在返回的结果集中要求额外的列:

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")

这会生成以下 SQL:

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

这篇关于如何按 has_many 关系中的对象数量对 Rails AR.find 进行排序的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！