Devise gem: add module after initial install

This may not be Devise specific but I'm wondering how to add an additional module to a gem that has already been installed when the initial install didn't include said module? In the case of Devise the migration helper t.confirmable is useful in the initial migration's Self.up method and the whole User table is torn down in the Self.down. My Rails-fu isn't strong enough to uncover what the t.confirmable helper is actually doing...

What happens when the User table already exists and you want to add something like :confirmable or :token_authenticatable? Obviously you can't just create_table(:users) again... so me thinks I want to add_column :users, ... and remove_c开发者_运维知识库olumn :users, ... but how do we go about finding out what needs to happen?

Take a look at Devise::Schema

https://github.com/plataformatec/devise/blob/master/lib/devise/schema.rb

which has this

# Creates confirmation_token, confirmed_at and confirmation_sent_at.
    def confirmable
      apply_devise_schema :confirmation_token,   String
      apply_devise_schema :confirmed_at,         DateTime
      apply_devise_schema :confirmation_sent_at, DateTime
    end

and then

https://github.com/plataformatec/devise/blob/master/lib/devise/orm/active_record.rb

def apply_devise_schema(name, type, options={})
    column name, type.to_s.downcase.to_sym, options
end

So in your migration just do

 add_column :users, :confirmation_token, :string
 add_column :users, :confirmed_at, :datetime
 add_column :users, :confirmation_sent_at, :datetime 

and the opposite for the down..

Your migration:

  class DeviseAddConfirmable < ActiveRecord::Migration
     def change
       change_table(:users) do |t|
          t.confirmable
       end

       add_index :users, :confirmation_token,   :unique => true
     end
  end