订购产品由协会计数belongs_to的

Question

类销售

belongs_to :product, :accessible => true 
belongs_to :brand, :accessible => true 

end 

Class Product 

has_many :sales 
belongs_to :brand 

end 

Class Brands 

has_many :products 
    has_many :sales 

end 

我要如何拥有最产品销售的品牌？

Answer 1

如果你想留在ActiveRecord的，你可以使用Calculations但需要2个查询来完成它：

>> brands = Sale.count(:id, :include => :brand, :group=> 'sales.brand_id', :limit => 5) 
    SQL (0.7ms) SELECT count(DISTINCT `sales`.id) AS count_id, sales.brand_id AS sales_brand_id FROM `sales` LEFT OUTER JOIN `brands` ON `brands`.id = `sales`.brand_id GROUP BY sales.brand_id LIMIT 5 
=> #<OrderedHash {967032312=>3, 1392881137=>1}> 

>> brands_with_most_sales = Brand.find(brands.keys) 
    Brand Load (0.5ms) SELECT * FROM `brands` WHERE (`brands`.`id` = 967032312) 
=> [#<Brand id: 967032312, title: "brand-x", created_at: "2009-11-19 02:46:48", updated_at: "2009-11-19 02:46:48">] 

否则你可能想使用你写自己的查询find_by_SQL