Mongoose不会返回自定义ID

我有一个集合,在mongo中包含一系列问题.

questions:[
{ 
  "_id" : 1,
  "question" : "Some question",
  "type" : "type"
}]

我已经定义了这样的架构:

var schema = mongoose.Schema({
  question: String
, type: String
})

var Model = mongoose.model('question', schema)

并在查询之后:

new Model.find({}, function(err,records) {
  console.log(records[0]._id)
  res.render('question/index', {title: 'question', question: records})
})

我undefined上了控制台或null(如果ID为0).