Keith Schacht’s Weblog

💡 TIL: Rails migrations can include an up_only part

29th October 2024

When writing a migration in Rails and you need to do one thing which can’t be automatically reversed, I always convert a def change to up and down. It turns out you can slip in an up_only block:

class AddFieldsToUsers < ActiveRecord::Migration[7.1]
  def change
    add_column :users, :first_name, :string
    add_column :users, :last_name, :string

    up_only do
      User.delete_all
    end
  end
end