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外部キーをreferences型カラムで保存する

Last updated at Posted at 2015-09-01

使い方

refernces型は外部キーを追加する時に使います
今回はtweetsモデルにuser_idを追加します。(user has_many tweet)

class CreateTweets < ActiveRecord::Migration
  def change
    create_table :tweets do |t|
      t.string :text
      t.references :user

      t.timestamps
    end
    add_index :tweets, [:user_id, :created_at]
  end
end

belongs_toreferencesのエイリアスなので、

t.references :user

t.belongs_to :user

とすることもできます。

実践例

###テーブル作成時

rails g model Tweet user:references
とすれば、

class CreateTweets < ActiveRecord::Migration
  def change
    create_table :tweets do |t|
      t.references :user, index: true

      t.timestamps
    end
  end
end

一発で出してくれます。ちなみにreferencesbelongs_toに入れ替えても同じです。

カラム追加時

rails g migration AddUserRefToTweets user:references

で、

class AddUserRefToTweets < ActiveRecord::Migration
  def change
    add_reference :tweets, :user, index: true
  end
end

とできます。

##注意
referencesbelongs_toを使うときは、カラムネームを指定する際に_id接尾子をつけません。

##参考
http://tkymtk.hatenablog.com/entry/rails-4-three-way-to-write-migration-2014-1

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