node.js – 具有引用数组的Mongoose模型模式：CastError：对于值“[object Object]”,Cast to ObjectId失败

我用express.js和mongoosejs建立了一个博客网站.一篇文章可能有一个或多个类别.当我创建一篇新文章时,我收到错误：

{ [CastError: Cast to ObjectId Failed for value "[object Object]" at path "categories"]
  message: 'Cast to ObjectId Failed for value "[object Object]" at path "categories"',name: 'CastError',type: 'ObjectId',value: [ [object Object] ],path: 'categories' }

任何人都可以帮助我吗？
相关代码如下：

Article模型定义如下：

var mongoose = require('mongoose'),scheR_884_11845@a = mongoose.scheR_884_11845@a;
var ArticlescheR_884_11845@a = new scheR_884_11845@a({
created: {  type: Date,default: Date.Now},title: String,content: String,sumMary: String,categories: [{ 
    type: scheR_884_11845@a.objectId,ref: 'Category' }]
});
mongoose.model('Article',ArticlescheR_884_11845@a);

而CAtegory模型的定义如下：

var mongoose = require('mongoose'),scheR_884_11845@a = mongoose.scheR_884_11845@a;
var CategoryscheR_884_11845@a = new scheR_884_11845@a({
  parent: {
    type: scheR_884_11845@a.objectId,},name: String,subs: [CategoryscheR_884_11845@a]
});
mongoose.model('Category',CategoryscheR_884_11845@a);

当我创建一篇新文章并将其保存为：

exports.create = function(req,res) {
  console.log(req.body);
  var article = new Article(req.body);
  article.user = req.user;
  console.log(articlE);
  article.save(function(err) {
    if (err) {
        console.log(err);
        return res.jsonp(500,{
            error: 'CAnnot save the article'
        });
    }
    res.jsonp(articlE);
  });
};

当调用create函数时,console.log()输出显示如下：

// console.log(req.body);
{ title: 'This is title',content: '<p>content here</p>',categories:
   [ { _id: '53c934bbf299ab241a6e0524',name: '1111',parent: '53c934b5f299ab241a6e0523',__v: 0,subs: [],sort: 1 } ],updated: [ 1405697477413 ] }

// console.log(articlE);
{ 
  title: 'This is title',_id: 53c93dc5b1c3b8e80cb4936b,categories: [],created: Fri Jul 18 2014 23:31:17 GMT+0800 (中国标准时间) }

// console.log(err);
{ [CastError: Cast to ObjectId Failed for value "[object Object]" at path "categories"]
  message: 'Cast to ObjectId Failed for value "[object Object]" at path "categories"',path: 'categories' }

我google了很多,但没有运气.请帮我！

更新：
感谢Gergo的回答.
但是,如果我用almoset更新存在的文章相同的代码,它的工作正常！为什么？代码显示如下：

var mongoose = require('mongoose'),Category = mongoose.model('Category'),_ = require('lodash');

exports.update = function(req,res) {
console.log(req.body);
var article = req.article;
article = _.extend(article,req.body);
console.log(articlE);
article.save(function(err) {
    if (err) {
        return res.jsonp(500,{
            error: 'CAnnot update the article'
        });
    }
    res.jsonp(articlE);

  });
};

输出如下：

// console.log(req.body);
{ _id: '53ca42f418bfb23c1e04df02',sumMary: 'tttt',title: 'tt',content: '<p>tttt</p>',__v: 2,categories: [ { _id: '53c934bbf299ab241a6e0524',name: '1111' } ],created: '2014-07-19T10:05:40.183Z'
}

// console.log(articlE);
{ _id: 53ca42f418bfb23c1e04df02,categories: [ { _id: 53c934bbf299ab241a6e0524,sort: 0
    } ],created: Sat Jul 19 2014 18:05:40 GMT+0800 (中国标准时间) 
}

这很好用.

var ArticlescheR_884_11845@a = new scheR_884_11845@a({
  ...
  categories: [{ 
    type: scheR_884_11845@a.objectId,ref: 'Category' }]
});

categories:
   [ { _id: '53c934bbf299ab241a6e0524',sort: 1 } ]

{ title: 'This is title',categories: [ '53c934bbf299ab241a6e0524' ],updated: [ 1405697477413 ] }