如何为具有相同关系的两个外键的模型编写关联？

Question

我一直在回到一个我自己没有解决的问题。我有一个 shipments table，其中有两列用于 addresses，即 to_address_id 和 from_address_id。

看了一个相关问题（），还是一头雾水。到目前为止，这是我的工作。我没有运行迁移。我试图在脑海中解决这个问题，然后再为此努力并浪费一两个小时。真的很感谢你的帮助。

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

Answer 1

如果我理解正确的话，你想在运输中添加始发地和目的地地址，对吗？

在这种情况下：

如果要创建迁移以创建关系

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

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

Answer 2

我不需要迁移，因为外键已经就位。我试过的那个没有用，strong_migrations gem 在抱怨。我只需要正确连接即可。

我想展示我如何避免一些混乱，所以我可以键入 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

如何为具有相同关系的两个外键的模型编写关联？

How to write associations for a model with two foreign keys for the same relationship?

postgresql

ruby-on-rails

foreign-keys

rails-migrations