can display relation between author

app/models/user/co_author.rb

@@ -6,9 +6,8 @@ class CoAuthor
   field :name_id, type: BSON::ObjectId
   field :co_author, localize: true
   field :email
-  field :type
 
-  has_and_belongs_to_many :co_author_relations
+  belongs_to :co_author_relations
 
   VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/
   validates :email, format: { with: VALID_EMAIL_REGEX },