查询（M：N）由关系有序属性

Question

我有一个简单许多一对多ER说明如下：

型号order.rb：

class Order < ActiveRecord::Base 
    has_many :cronologies 
    has_many :statuses, :through => :cronologies 
end 

型号cronology.rb：

class Cronology < ActiveRecord::Base 
    belongs_to :order 
    belongs_to :status 
    validates_uniqueness_of :order_id, :scope => :status_id 
end 

型号status.rb：

class Status < ActiveRecord::Base 
    has_many :cronologies 
    has_many :orders, :through => :cronologies 
end 

钍下面的代码让我获得分配给订单的所有状态。

@order.statuses 

......但如何获得按照cronology表的“created_at”属性排序的状态？

Answer 1

@order.statuses.all(:order => "cronologies.created_at") 

或者如果您总是希望以这种方式订购它，请将其关联。

class Order < ActiveRecord::Base 
    has_many :cronologies 
    has_many :statuses, :through => :cronologies, :order => "cronologies.created_at" 
end