Node.js 有条件地将_id字段添加到mongoose模型

我有以下代码：

var concert = new models.concert({
    name: request.body.name,
    date: request.body.date,
    city: request.body.city,
    location: request.body.location,
    programme: request.body.programme
});
console.log("<< Concert to attempt save on: " + concert);
if (request.body._id) {
    console.log("Received _id field from body: " + request.body._id);
    concert._id = ObjectId(request.body._id + '');
}

var concert=new models.concert({
名称：request.body.name，
日期：request.body.date，
城市：request.body.city，
位置：request.body.location，
节目：request.body.program
});
控制台日志（“
<< Concert to attempt save on: 
{ 
    _id: 572312a289a4d8d810eed717,
    programme: 'to be announced',
    location: 'J.Nepomuk-Kapelle',
    city: 'Vienna, Austria32',
    date: 1464382800,
    name: 'Chamber Music Concert' 
}