使用关系表列更新父表列 - Parse.com作业

Question

我已经编写了云作业，这将更新上次评论论坛的日期，在论坛栏目中进行了最后更新：

Parse.Cloud.job("MigrateupdatedAtForumCommenttoForum", function(status) {  
    var ForumQuery = new Parse.Query('Forum');
    ForumQuery.descending('updatedAt');
    ForumQuery.limit(1000);
    ForumQuery.greaterThan('comment_count',0);
    ForumQuery.find().then(function(forums) {        
        for (var i=0; i<forums.length; i++) {
            //var ForumComment = forums[i].relation('forum_comment');
            var ForumCommentQuery = forums[i].relation('forum_comment').query();
            ForumCommentQuery.descending('updatedAt');
            ForumCommentQuery.first().then(function (comment) {
                if (comment != null) {
                    forums[i].set('lastupdatedat', comment.updatedAt);
                    forums[i].save();

                } else {
                    forums[i].set('lastupdatedat', forum.updatedAt);
                    forums[i].save();
                }
            });               
        }
        status.success('Transfer Completed!');
    }, function(error) {
        status.success('Error in Transfer column data');
    });
});

当我在Parse Job中托管它并执行预定作业时，给我错误。

错误详情如下：

E2015-10-09T09:32:03.990Z]v41 Ran job MigrateupdatedAtForumCommenttoForum with:
  Input: {}
  Result: TypeError: Cannot call method 'query' of undefined.
    at new e (Parse.js:14:29896)
    at e.<anonymous> (main.js:877:28)
    at e.s (Parse.js:14:26859)
    at e.n.value (Parse.js:14:26278)
    at e.<anonymous> (Parse.js:14:26931)
    at e.s (Parse.js:14:26859)
    at Parse.js:14:27245
    at i (Parse.js:14:27200)
    at e.n.value (Parse.js:14:27230)
    at e.s (Parse.js:14:26905)

我无法在Parse上运行代码作为云作业。当我在我的代码中编写函数时工作正常。