向现有 Rails 模型添加模型引用 [英] Adding a Model Reference to existing Rails model

问题描述

我想知道在 Rails 3 中添加两个现有类之间关系的正确"方法.

I'd like to know the "proper" way to approach adding a relation between two existing classes in Rails 3.

鉴于现有模型:小丑和兔子

Given existing models: Clown & Rabbit

我想添加一个从 Rabbit 到 Clown 的引用 (belongs_to).我首先尝试生成迁移:

I'd like to add a reference (belongs_to) from Rabbit to Clown. I start by trying to generate a migration:

rails g migration AddClownToRabbits clown:reference

这给了我一个看起来像这样的迁移:

which gives me a migration that looks like:

class AddClownToRabbits < ActiveRecord::Migration
  def self.up
    add_column :rabbits, :clown, :reference
  end

  def self.down
    remove_column :rabbits, :clown
  end
end

在此迁移中 rake db:migrate 之后，我检查 SQLite3 的 development.db 并看到一个新列:小丑"参考

After rake db:migrate on this migration I examine SQLite3's development.db and see a new column: "clown" reference

我想我期待一个 "clown_id" 整数 列和一个看起来像这样的迁移:

I guess I was expecting a "clown_id" integer column and a migration that looked like:

class AddClownToRabbits < ActiveRecord::Migration
  def self.up
    add_column :rabbits, :clown_id
  end

  def self.down
    remove_column :rabbits, :clown_id
  end
end

我确定 :reference 应该等同于t.references :clown"，但我找不到文档(大吃一惊).API 说 add_column: 为表实例化一个新列.type 参数通常是迁移原生类型之一，它是以下之一::primary_key、:string、:text、:integer、:float、:decimal、:datetime、:timestamp、:time、:date, :二进制，:boolean.

I'm sure :reference is supposed to be equivalent to "t.references :clown" but I can't find the documentation (big surprise). API says add_column: Instantiates a new column for the table. The type parameter is normally one of the migrations native types, which is one of the following: :primary_key, :string, :text, :integer, :float, :decimal, :datetime, :timestamp, :time, :date, :binary, :boolean.

...没有 reference 到 :reference.

...with no reference to :reference.

推荐答案

在 Rabbit 中设置belongs_to，在Clown 中设置has_many 后，您可以进行迁移:

After you set belongs_to in Rabbit, and has_many in Clown, you can do a migration with:

add_column :rabbit, :clown_id, :integer

请参阅 Paulo's answer below 以获得更新的答案(Rails 4+)

See Paulo's answer below for a more updated answer (Rails 4+)

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