searches the universe with the given index from read() and adds it to the entities connected to the entity
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);
      }