ROR中，多重一对多的关系应该怎么用:through来表示啊？

比如模型是这样：
[code="ruby"]
class Province < ActiveRecord::Base

has_many :cities

end

class City < ActiveRecord::Base

has_many :factories

belongs_to :province
end

class Factory < ActiveRecod::Base

has_many :products
belongs_to :city
end

class Product < ActiveRecord::Base

belongs_to :factory
end
[/code]
是不是应该直接弄一个:through来表示Product和Province之间的关联呢？可是这样的:through怎么写啊？我试了半天都不中啊……

主要我是想查找Product表里面，Province包含某字符的记录，不用:through而用别的方法，能达到目的也行……

1. class Province < ActiveRecord::Base
   
2. has_many :cities
   
3. has_many :products through :cities
4. end
   
5. 
   
6. class City < ActiveRecord::Base
   
7. has_many :factories
   
8. belongs_to :province has_many :products throught:factories
9. end
   
   1. 
      
   2. class Factory < ActiveRecod::Base
      
   3. has_many :products
      
   4. belongs_to :city
      
   5. end
      
   6. 
      
   7. class Product < ActiveRecord::Base
      
   8. belongs_to :factory
      
   9. end

试试看。

[code="ruby"]
class Province < ActiveRecord::Base

has_many :cities

end

class City < ActiveRecord::Base

has_many :factories

belongs_to :province
end

class Factory < ActiveRecod::Base

has_many :products
belongs_to :city
end

class Product < ActiveRecord::Base

belongs_to :factory
end
[/code]