如何根据关联顺序定义命名范围答案

【问题标题】：How define named scoped with order on associations如何根据关联顺序定义命名范围
【发布时间】：2014-01-23 18:28:00
【问题描述】：

我有两个模型。

 class Shoe < ActiveRecord::Base     
   has_many :sizes, :dependent => :destroy
   scope :brand_asc , order('brand ASC')  
   scope :brand_desc , order('brand DESC')
   attr_accessible :brand ,:model
 end


 class Size < ActiveRecord::Base
   belongs_to :shoe
   scope :size_brand_asc , order("#{self.shoe.brand} ASC")
   scope :size_brand_desc , order("#{self.shoe.brand} DESC")             
 end

It is very easy to call named scope on Shoe model like below.

  @shoes = Shoe.brand_asc

But i want to sort sizes on the base of "brand" that is attribute of shoe model.so this

对我不起作用，如下所示。

   @sizes = Size.size_brand_asc  # giving error

我如何根据鞋子品牌对尺码进行排序

【问题讨论】：

标签： ruby-on-rails named-scope

【解决方案1】：

您可以通过以下方式实现此目的：

class Size < ActiveRecord::Base
  belongs_to :shoe
  scope :brand_ordered, lambda do |way = 'ASC'| 
    includes(:shoe).order("shoes.brand #{way}")
  end

用法：

@sizes = Size.brand_ordered('DESC')
# or
@sizes = Size.brand_ordered('ASC')
# equivalent:
@sizes = Size.brand_ordered

在鞋类中：

class Shoe < ActiveRecord::Base
  scope :brand_ordered, lambda do |way = 'ASC'| 
    order("#{self.table_name}.brand #{way}")
  end

【讨论】：

【解决方案2】：

一行回答

scope :size_brand_asc, ->{joins(:shoe) & Shoe.brand_asc}

【讨论】：