引用另一个模型时猫鼬填充不起作用

Question

我一直在尝试在评论模型中引用用户模型。我已确保一切都已检查完毕，但仍然无法正常工作。

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const commentSchema = mongoose.Schema({
  writer: {
    type: Schema.Types.ObjectId,
    ref: 'User'
  },
  postId: {
    type: String,
  },
  responseTo: {
    type: Schema.Types.ObjectId,
    ref: 'User'
  },
  content: {
    type: String
  }

}, { timestamps: true })


const Comment = mongoose.model('Comment', commentSchema);

module.exports = { Comment }

我在这里引用用户模型是因为我需要从中获取一些字段。

router.post("/saveComment", auth, (req, res) => {

  const comment = new Comment(req.body)

  comment.save((err, comment) => {
    if (err) return res.json({ success: false, err })
     
    //send newly saved comment inside parent cmp
    Comment.find({ '_id': comment._id })
      .populate('writer')
      .exec((err, result) => {
        if (err) return res.json({ success: false, err })
        return res.status(200).json({ success: true, result })
      })

  })

})

向该端点发出请求会返回结果，但会忽略我对用户模型的引用

{
    "success": true,
    "result": [
        {
            "_id": "60527698499c27244c9e9f4c",
            "content": "Comment 1",
            "createdAt": "2021-03-17T21:37:28.463Z",
            "updatedAt": "2021-03-17T21:37:28.463Z",
            "__v": 0
        }
    ]
}