Question

您好我正在寻找一种方法来查询这4个表，以获得与rails 4中用户选择的类别匹配的唯一产品。

Rails模型

class User < ActiveRecord::Base
  has_many :categories, through: :user_categories
  has_many :user_categories
end

class Product < ActiveRecord::Base
  has_many :categories, through: :product_categories
  has_many :product_categories
end

class Category < ActiveRecord::Base
  has_many :users
  has_many :products
end

class UserCategory < ActiveRecord::Base
  belongs_to :user
  belongs_to :category
end

class ProductCategory < ActiveRecord::Base
  belongs_to :product
  belongs_to :category
end

表格结构

products             
+---------------+      
| id | name     |   
+---------------+ 
| 1  | mouse    | 
| 2  | keyboard | 
| 3  | iphone 6 | 
+---------------+ 

categories
+---------------+
| id | name     |
+---------------+
| 1  | computer |
| 2  | mobile   |
+---------------+

users
+-----------+
| id | name |
+-----------+
| 1  | foo  |
| 2  | bar  |
+-----------+

product_categories
+------------------+
| id | p_id | c_id |
+------------------+
| 1  |   1  |   1  |
| 2  |   3  |   2  |
+------------------+

user_categories
+------------------+
| id | u_id | c_id |
+------------------+
| 1  |   1  |  1   |
+------------------+

Answer 1

你的意思是这样的？

@user_categories_ids = User.first.categories.map(&:id)

Product.includes(:categories).where(categories: { id: @user_categories_ids })

如果您已正确设置关联，这应该有效。

如果您之后未使用类别关联，那么在性能方面，最好使用joins()或joins().distinct()代替includes()

联接示例：

Product.joins(:categories).where(categories: { id: @user_categories_ids })

如果您想要独特的结果

Product.joins(:categories).where(categories: { id: @user_categories_ids }).distinct # .uniq should also work I guess.

rails查询多个表虽然有很多关系

1 个答案: