限制 has_many 中返回的对象数量 [英] limit the number of objects returned in a has_many

问题描述

如何限制在有很多关系中返回的行数?例如:

How can I limit the number of rows returned in a has many relationship? For example:

class User < ActiveRecord::Base
  has_many :photos
end

我希望能够做到:

User.includes(:photos => {:limit => 8}).all

这显然不起作用，但具有此功能的东西.我需要自己写出 SQL 吗?

This obviously doesnt work, but something with this functionality. Do I need to write out the SQL myself?

提前致谢！

我不想限制关联，只是查询结果.所以一个用户可能有一千张照片，我只想要返回前三张.

I dont want to limit the association, just the query results. So a User might have a thousand photos, I only want the top 3 returned.

推荐答案

只需为 has_many 关联添加一个限制选项:

Just add a limit option to the has_many association:

class User < ActiveRecord::Base
  has_many :photos, :limit => 8
end

编辑

根据您的需要:

class User < ActiveRecord::Base
  has_many :all_photos, :class_name => "Photo"
  has_many :photos, :limit => 8
end

注意:在 all_photos 关联中将class"更改为class_name"

这篇关于限制 has_many 中返回的对象数量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！