add preferred name when create user

app/models/user.rb

@@ -4,7 +4,7 @@ class User < ActiveRecord::Base
   devise :database_authenticatable, :registerable,
          :recoverable, :rememberable, :trackable, :validatable
 
-  before_save :set_avatar
+  before_save :set_avatar, :set_preferred_name
 
   after_save :ensure_authentication_token
 
@@ -31,6 +31,10 @@ class User < ActiveRecord::Base
     self.avatar = Gravatar.new(self.email).image_url
   end
 
+  def set_preferred_name
+    self.preferred_name = email.split('@')[0]
+  end
+
 
   def self.create_user(name, avatar)
     User.create name: name, avatar: avatar