add co-author db and curd page, but it can't destory it...

app/models/user/co_author.rb

@@ -0,0 +1,19 @@
+class CoAuthor
+  include Mongoid::Document
+
+  LANGUAGE_TYPES = [ "English", "Chinese" ]
+
+  field :name_id, type: BSON::ObjectId
+  field :co_author, localize: true
+  field :email
+  field :type
+
+
+  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
+  validates :email, format: { with: VALID_EMAIL_REGEX },
+             uniqueness: { case_sensitive: false }
+
+  validates :co_author, presence: true
+  before_save { |coauthor| coauthor.email = email.downcase }
+end
+