Add UserAttribute model, suppose it will store user model want to use which attribute group

app/models/user.rb

@@ -3,4 +3,6 @@ class User
  
   devise :authenticatable, :recoverable, :rememberable, :trackable
   
+  key :use_attributes
+    
 end

app/models/user_attribute.rb

@@ -0,0 +1,9 @@
+class UserAttribute
+  
+  include MongoMapper::Document
+  
+  key :ident, String
+  key_i18n :name, String
+  key_i18n :attrs, Array
+  
+end