一种方式有很多通过

Question

我有一个类别,一个子类别和一个产品模型.

我有:

Category has_many Subcategories
Subcategory has_many Products
Subcategory belongs_to Category
Product belongs_to Subcategory

有没有办法有类似的东西

Category has_many Projects through Subcategories

？

"普通"轨道方式不起作用,因为"子类别"不属于产品,因此产品没有子类别_id字段.相反,我需要查询类似的东西

SELECT * FROM products WHERE id IN category.subcategory_ids

有没有办法做到这一点？

谢谢,

NicolásHockIsaza

Answer 1

如果你使用'正常'的Ruby on Rails方式,你描述的数据库看起来就像这样.如果您的数据库不是这样构建的,我建议您阅读更多关于如何在Ruby on Rails中完成关联的内容,因为这是正确的方法(并且您应该t.references :category在迁移中使用它,因为它的设计目的是为了不容易弄乱你的参考文献).

+----------------+  +----------------+ +----------------+
| categories     |  | subcategories  | | products       |
+----------------+  +----------------+ +----------------+
| id             |  | id             | | id             |
| ...            |  | category_id    | | subcategory_id |
|                |  | ...            | | ...            |
+----------------+  +----------------+ +----------------+

以此作为您的数据库结构,has_many :products, :through => subcategories适用于Category模型.

Category.rb

class Category < ActiveRecord::Base
  has_many :subcategories
  has_many :products, :through => :subcategories
end

Subcategory.rb

class Subcategory < ActiveRecord::Base
  belongs_to :category
  has_many :products
end

Product.rb

class Product < ActiveRecord::Base
  belongs_to :subcategory
  has_one :category, :through => :subcategory  # don't need this, but it does work
end

ruby脚本\控制台

>> c = Category.create
=> #<Category id: 1, ...>
>> c.subcategories.create
=> #<Subcategory id: 1, category_id: 1, ...>
>> p = s.products.create
=> #<Product id: 1, subcategory_id: 1, ...>
>> c.products
=> [#<Product id: 1, subcategory_id: 1, ...>]
>> p.category         # if you have the has_one assocation
=> #<Category id: 1, ...>