基于枚举值的自定义顺序

Question

我为角色定义了枚举：

enum role: {ordinary: 0, manager: 1, admin: 2}

我想按以下顺序订购一组对象：

admin (first all admins)
ordinary (then all ordinaries)
manager (and lastly all managers)

这可能吗？

Answer 1

解决方案：

class YourModel < ActiveRecord::Base
  ROLE_ORDERS = [2, 0, 1]

  scope :order_by_role, -> {
    order_by = ['CASE']
    ROLE_ORDERS.each_with_index do |role, index|
      order_by << "WHEN role=#{role} THEN #{index}"
    end
    order_by << 'END'
    order(order_by.join(' '))
  }
end

那么你的查询就很简单了：

YourModel.order_by_role

生成的查询是：

SELECT * from your_models
ORDER BY ( CASE
           WHEN role=2 THEN 0
           WHEN role=0 THEN 1
           WHEN role=1 then 2
           END
         )

来自 this

的良好参考

Answer 2

感谢 this answer 我想到了这个：

order("role = 0 DESC, role = 1 DESC, role = 2 DESC")

或者，作为具有可选参数的范围：

scope :order_by_roles, -> (first = :admin, second = :ordinary, third = :manager) { 
  order("role = #{User.roles[first]} DESC, role = #{User.roles[second]} DESC, role = #{User.roles[third]} DESC") 
}

Answer 3

从 Rails 6.0 开始，将抛出此弃用警告："Dangerous query method (method whose arguments are used as raw SQL) called with non-attribute argument(s) [..] Non-attribute arguments will be disallowed in Rails 6.1. This method should not be called with user-provided values, such as request parameters or model attributes. Known-safe values can be passed by wrapping them in Arel.sql()."

因此，在他的回答和的基础上，我建议：

class YourModel < ActiveRecord::Base
  ROLE_ORDERS = [2, 0, 1]
  scope :order_by_role, -> { order(Arel.sql(ROLE_ORDERS.map{ |role| "role=#{role} DESC" }.join(', '))) }
end

然后在您的代码中使用它，就像 ...

YourModel.order_by_role

... 生成此查询：

SELECT * from your_models
ORDER BY role = 2 DESC, role = 0 DESC, role = 1 DESC

Answer 4

ActiveRecord::QueryMethods#in_order_of (Rails 7+)

从Rails7开始，有新方法ActiveRecord::QueryMethods#in_order_of.

来自官方 Rails 文档的引用：

in_order_of(column, values)

Allows to specify an order by a specific set of values. Depending on your adapter this will either use a CASE statement or a built-in function.

User.in_order_of(:id, [1, 5, 3])
# SELECT "users".* FROM "users" ORDER BY FIELD("users"."id", 1, 5, 3)

它也适用于模型枚举：

class Book < ApplicationRecord
  enum status: [:proposed, :written, :published]
end

Book.in_order_of(:status, %w[written published proposed])

来源：

官方文档 - ActiveRecord::QueryMethods#in_order_of.
PR - Add ActiveRecord::QueryMethods#in_order_of.
More examples.

基于枚举值的自定义顺序

Custom order based on Enum values

enums

activerecord

ruby-on-rails

rails-activerecord

ruby-on-rails-5

ActiveRecord::QueryMethods#in_order_of (Rails 7+)