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Rails 4:推荐模型关联

associations ruby-on-rails-4 ruby-on-rails

Jeremy Thomas · 技术社区 · 8 年前

referral client 但是我想知道如何正确设置 送交 模型,以便我可以查询:

Client.find(x).referrals
# returns all referrals where referrer has the client's id

Client.find(x).referred_by
# returns client that referred this client

2 回复 | 直到 8 年前

max Mike Williams 8 年前

将两个关联设置到同一个表是ActiveRecord中最复杂的关联之一。关键是为每个外键列设置不同的关联。

因此,让我们从连接表开始:

# This is a Rails 5 migration - don't copy paste it
# You'll have to generate one for rails 4
class CreateReferrals < ActiveRecord::Migration[5.0]
  def change
    create_table :referrals do |t|
      t.belongs_to :referrer_id, foreign_key: false
      t.belongs_to :referred_id, foreign_key: false
      # Since the table for the foreign key cannot be automatically derived you need to add them manually
      add_foreign_key :referrals, :clients, column: :referrer_id
      add_foreign_key :referrals, :clients, column: :referred_id
      t.timestamps
    end
  end
end

class Referral < < ActiveRecord::Base
  belongs_to :referrer, class_name: 'Client'
  belongs_to :referred, class_name: 'Client'
end

这里还没什么可怕的。 class_name: 'Client' 告诉ActiveRecord(AR)关联指向哪个表,因为它不能从关联的名称派生。现在,让我们在客户端上创建反向关联:

class Client < ActiveRecord::Base
  has_many :referrals, class_name: 'Referral', 
    foreign_key: 'referrer_id'
  has_many :referrals_as_referred, class_name: 'Referral', 
    foreign_key: 'referred_id'
end

要将关联添加到被引用或引用到客户端的其他客户端,请使用间接关联:

class Client < ActiveRecord::Base
  # ...
  # clients reffered by this client
  has_many :referred_clients, 
        through: :referrals,
        source: :referred
  has_many :referrers, 
        through: :referrals_as_referred,
        source: :referrer
end

through: :referrals 告诉AR通过名为 :referrals .
source: :referred

Ajinath Jedhe 8 年前

您可以为此使用自关联。在客户端模型上,添加referrals\u id列。客户端模型中的关联如下:

class Client < ActiveRecord::Base
  has_many :referrals, class_name: "Client", foreign_key: :referrals_id
  belongs_to :referred_by, class_name: "Client", foreign_key: :referrals_id
end

假设您在表中有这两条记录。

[{  
   "id":1,
   "name":"Admin",
   "referrals_id": nil,
 },
 {  
   "id":2,
   "name":"Client",
   "referrals_id":1,
 }]

Client.find(1).referrals

这将生成类似以下的SQL:

`SELECT "clients".* FROM "clients" WHERE "clients"."referrals_id" = ?  [["referrals_id", 1]]`

for refered\u by will返回引用此客户端的客户端

Client.find(2).referred_by

这将生成类似以下内容的SQL:

SELECT  "clients".* FROM "clients" WHERE "clients"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]