Ruby On Rails设计：如何在注册期间避免重复的用户名

Hi I am very new to Ruby on Rails and Devise, and I would like to know how I can configure devise to disallow a user from signing up with a username that is already taken. The initial configuration is to not allow a taken email during signup, but I want this same configuration for my newly created username field. I already added Hi I am very new to Ruby on Rails and Devise, a