when delete co-author relation, the co-author will be reset nil

app/helpers/desktop/co_author_relations_helper.rb

@@ -1,2 +1,8 @@
 module Desktop::CoAuthorRelationsHelper
+  def reset_co_author_relation relation
+    co_author = CoAuthor.where(co_author_relations_id: relation)
+    co_author.map do |c|
+      co_author.update_attributes(co_author_relations_id: nil)
+    end
+  end
 end