code: function(postIds) {
          if (!postIds) return;
  
          var updatedRelations = [];
          // create new relations for that post ids that were not added yet
          _.each(postIds, function(postId) {
            var relation = _.find(that.relations(), function(relation) {
              return ko.unwrap(relation.relatedPost.id) == postId;
            });
  
            if (!relation) {
              var post = findPost(postId);
  
              relation = {
                relatedPost: post,
                priority: ko.observable(null),
                id: ko.observable(null)
              };
            }
  
            updatedRelations.push(relation);
          });
  
          that.relations(updatedRelations);
        }
docs: searches the universe with the given index from read() and adds it to the entities connected to the entity