can select relection from relation db

app/models/user/user.rb

@@ -3,7 +3,7 @@ class User
   include Mongoid::Document
   include Mongoid::Timestamps
 
-  devise :database_authenticatable, :recoverable, :rememberable, :trackable, :registerable, :timeoutable
+  devise :database_authenticatable, :recoverable, :rememberable, :trackable, :registerable, :validatable, :timeoutable
   
   mount_uploader :avatar, AvatarUploader
   
@@ -194,4 +194,4 @@ class User
     end
   end
 
-end
+end