範圍在Rails和嵌套查詢

Question

Possible Duplicate:
Unable to join self-joins tables in Rails

我多類別

class Category < ActiveRecord::Base 
    belongs_to :parent, :class_name => "Category", :foreign_key => "parent_id" 
    has_many :children, :class_name => "Category" 
    has_many :products 
    attr_accessible :description, :title, :parent 

end 

這裏是Product

class Product < ActiveRecord::Base 
    belongs_to :category 
end 

一個模式，我需要在Product定義範圍，能夠找到所有產品按父類別名稱

class Product < ActiveRecord::Base 
#..... 
#scope :of_tea, lambda{ where(:category.parent.name => "tea") } # not working 
end 

Answer 1

使用哈希指定where條件：

where(:category => { :parents => { :title => "tea" } })