Add Not Null Column to Existing Model

migration.rb

class AddPublishableToTimelinePage < ActiveRecord::Migration[5.0]
  def up
    add_column :timeline_pages, :published_at, :datetime
    add_column :timeline_pages, :status, :string, null: false, default: "draft"
    add_column :timeline_pages, :uuid, :text

    TimelinePage.update_all({
      published_at: Time.now,
      uuid: SecureRandom.uuid
    })
    change_column_null :timeline_pages, :published_at, false
    change_column_null :timeline_pages, :uuid, false

  end

  def down
    remove_column :timeline_pages, :published_at, :datetime
    remove_column :timeline_pages, :status, :string
    remove_column :timeline_pages, :uuid, :text
  end
end