return at_position_list for content json

models/comment.rb

@@ -44,7 +44,7 @@ class Comment < Content
     if params[:recursive]
       self.class.hash_tree(subtree(sort: sort_by_parent_and_time)).first
     else
-      as_document.slice(*%w[body course_id endorsed anonymous created_at updated_at])
+      as_document.slice(*%w[body course_id endorsed anonymous created_at updated_at at_position_list])
                   .merge("id" => _id)
                   .merge("user_id" => author.id)
                   .merge("depth" => depth)

models/comment_thread.rb

@@ -77,7 +77,7 @@ class CommentThread < Content
   end
 
   def to_hash(params={})
-    doc = as_document.slice(*%w[title body course_id anonymous commentable_id created_at updated_at])
+    doc = as_document.slice(*%w[title body course_id anonymous commentable_id created_at updated_at at_position_list])
                       .merge("id" => _id)
                       .merge("user_id" => author.id)
                       .merge("votes" => votes.slice(*%w[count up_count down_count point]))