如何为具有相同关系的两个外键的模型编写关联？答案

【问题标题】：How to write associations for a model with two foreign keys for the same relationship?如何为具有相同关系的两个外键的模型编写关联？
【发布时间】：2020-09-13 09:48:40
【问题描述】：

我又遇到了一个我自己还没有解决的问题。我有一个shipments 表，其中addresses 有两列，即to_address_id 和from_address_id。

看了一个相关的问题（Same Model for Two belongs_to Associations migration），我还是一头雾水。这是我到目前为止的工作。我还没有运行迁移。在为此烦恼并浪费一两个小时之前，我正试图在脑海中解决这个问题。非常感谢您的帮助。

class AddAddressFromAndAddressToToAddress < ActiveRecord::Migration[6.0]
  def change
    add_reference :address, :address_from, null: false
    add_reference :address, :address_to, null: false
    add_foreign_key :address, :shipments, column: :to_address_id
    add_foreign_key :address, :shipments, column: :from_address_id
  end
en

【问题讨论】：

标签： ruby-on-rails postgresql foreign-keys rails-migrations

【解决方案1】：

如果我理解正确，您想在运输中添加出发地和目的地地址，对吗？

在这种情况下：

如果要创建迁移来创建关系

class AddOriginAndDestinyAddressToShipment < ActiveRecord::Migration[6.0]
  def change
    add_reference :shipments, :from_address, foreign_key: { to_table: :addresses }
    add_reference :shipments, :to_address, foreign_key: { to_table: :addresses }
  end
end

如果你想创建一个有关系的模型

class CreateShipments < ActiveRecord::Migration[6.0]
  def change
    create_table :shipments do |t|
      t.datetime :deadline
      t.references :from_address, null: false, foreign_key: { to_table: :addresses }
      t.references :to_address, null: false, foreign_key: { to_table: :addresses }
      t.timestamps
    end
  end
end

并且模型Shipment必须是这样的

class Shipment < ApplicationRecord
  belongs_to :to_address, class_name: 'Address'
  belongs_to :from_address, class_name: 'Address'
end

【讨论】：

【解决方案2】：

我不需要迁移，因为外键已经到位。我试过的那个没有用，strong_migrations gem 在抱怨。我只需要正确接线即可。

我想展示我节省了一些混乱的方法，所以我可以输入 shipment.to_address 或 shipment.address_to 并获得相同的结果。谢谢。

class Shipment < ApplicationRecord
  belongs_to :address_from, class_name: 'Address', foreign_key: :from_address_id
  belongs_to :from_address, class_name: 'Address', foreign_key: :from_address_id
  belongs_to :address_to,   class_name: 'Address', foreign_key: :to_address_id
  belongs_to :to_address,   class_name: 'Address', foreign_key: :to_address_id
end

class Address < ApplicationRecord
  has_many :shipments
end

【讨论】：