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

问题描述

我如何限制在一个有很多关系，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

我希望能够做的：

I want to be able to do:

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

这显然是行不通的，但一些使用这一功能。我是否需要写出来的SQL自己？

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

在此先感谢！

编辑： 我不希望限制的关联，只是查询结果。因此，用户可能有上千张照片，我只希望前3回。

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

只需添加一个限制选项给的has_many关联：

Just add a limit option to the has_many association:

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

修改

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：改变阶级在all_photos协会将class_name

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