Devise: find by username OR email

devise.find_by_username_or_email.rb

class User
  extend ClassMethods

  devise :database_authenticatable, :omniauthable, :registerable, :confirmable, :recoverable, :rememberable

  module ClassMethods
    def find_for_database_authentication(conditions)
      value = conditions[authentication_keys.first]
      where(["username = :value OR email = :value", { :value => value }]).first
    end

    def send_reset_password_instructions(attributes={})
      super(authentication_attribute(attributes))
    end

    def send_confirmation_instructions(attributes={})
      super(authentication_attribute(attributes))
    end

    protected
      # determine email by username
      def authentication_attribute(attributes)
        user = self.find_by_username(attributes[:email])
        attributes[:email] = user[:email] if user
        attributes
      end
  end
end