ActiveRecord Migrations

Flashcard 6 of 6

Is there anything we could add to the following migration to ensure that actions will only be able to reference projects that actually exist in our system?

class CreateActions < ActiveRecord::Migration
  def change
    create_table :actions do |t|
      t.string :title
      t.references :project

      t.timestamps null: false
    end

    add_index :actions, :project_id
  end
end

Answer:

Reveal Answer

The migration could include a foreign key constraint that would enforce the Action -> Project relationship to ensure an Action can never point to a non-existent Project.

class CreateActions < ActiveRecord::Migration
  def change
    create_table :actions do |t|
      t.string :title
      t.references :project

      t.timestamps null: false
    end

    add_index :actions, :project_id
    add_foreign_key :actions, :projects
  end
end

Check out [our post on Rails Foreign Keys][] for more detail and tips on implementing foreign keys in your rails app.

Note Rails 4.2 has native support for foreign keys, but for prior versions of Rails you'll need to include the [Foreigner Gem][].

[our post on Rails Foreign Keys]: https://robots.thoughtbot.com/referential-integrity-with-foreign-keys [Foreigner Gem]: https://github.com/matthuhiggins/foreigner

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