如何使用超类中的属性对ActiveRecord结果进行排序？

Question

我有两个型号：

class Manufacturer < ActiveRecord::Base 
    has_many :models 
end 

class Model < ActiveRecord::Base 
    belongs_to :manufacturer 
    belongs_to :model 
end 

我想做什么就能做的是找到所有的制造商，其型号属于某一类别：

manufacturers = Model.find(:all, :conditions=>["vehicle_category_id = 1"], :include => :manufacturer, :group => "manufacturer_id").map {|model| model.manufacturer } 

但我希望能够订购结果按制造商名称即制造商。名称

你知道我该怎么做吗？

UPDATE：

这对我的作品，但似乎非常低效的，必须有更好的方式：

manufacturers = (Model.find(:all, :conditions=>["vehicle_category_id = 1"], :include => :manufacturer, :group => "manufacturer_id").map {|model| model.manufacturer }).compact.sort{|x,y| x.name <=> y.name} 

Answer 1

解决方案1 ​​

Manufacturer.all(
    :condition => [ "EXISTS (
        SELECT a.id 
        FROM models a 
        WHERE a.manufacturer_id  = manufacturers.id AND 
          a.vehicle_category_id = ? 
        )", 
        1 
       ], 
    :order  => "manufacturers.name" 
) 

解决方案2

Manufacturer.all(
    :select => "DISTINCT manufacturers.*", 
    :joins  => :models, 
    :condition => [ "models.vehicle_category_id = ?", 1], 
    :order  => "manufacturers.name" 
) 

• 解决方案2是使用钢轨结构。

• 溶液1比溶液更快2.