从子模型选择只有一行根据父模型 [英] Selecting only one row from child model based upon the parent model

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本文介绍了从子模型选择只有一行根据父模型的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

以下是2种型号之间的关联:

Following is the association between 2 models:

class FotoGossip < ActiveRecord::Base
   has_many :uploads
end

class Upload < ActiveRecord::Base
   belongs_to :foto_gossip
end

@latest_uploads = Upload.all(:include => :foto_gossip, :order => "created_at DESC", :limit => 5)

它会显示最新的5张照片,从上传模式。
但是,我想显示5图像从上传,ORDER_BY created_date DESC但人均FotoGossip只有1图像。
它像它的一张照片,从上传模式分组近期FotoGossip。

It displays the latest 5 photos from Upload model.
But, I want to display 5 images from Uploads, order_by created_date DESC but only 1 image per FotoGossip.
Its something like grouping the recent FotoGossip with its one photo from Uploads model.

推荐答案

这下AR查询解决了这个问题。

This following AR query solved it.

@latest_uploads = Upload.all(:include => :foto_gossip, :order => "created_at DESC", :limit => 5, :group => :foto_gossip_id)

神奇在于:组选项

The magic lies in the :group option.

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