mongoose populate 联表查询不起作用，求指点，困惑好几天了

Question

以下从建表到查询：

const mongoose = require('mongoose')
const Schema = mongoose.Schema
const ObjectId = Schema.Types.ObjectId

const ProductSchema = new mongoose.Schema({
    productName:String,
    productCatalog: {
        type: ObjectId,
        ref: 'ProductCatalog' //类目
    },
    productMainPicture:String,
    productPrice:Number,
    productTotal:Number,
    productSalesTotal:Number,
    productStatus:Boolean,
    productOrigin:String,      //产地
    brandName:{
        type: ObjectId,
        ref: 'Brand'           //品牌
    },
    createdAt: {
        type: Date,
        default: Date.now
    },
    updatedAt: {
        type: Date,
        defalut: Date.now
    }
});

module.exports = ProductSchema

Model

var mongoose = require('mongoose')
var ProductSchema = require('./../schemas/product')

var Product = mongoose.model('Product', ProductSchema)

module.exports = Product

查询

var express = require('express')
var productRouter = express.Router()
var Product = require('./../app/models/product')

productRouter.route(`/`)
.get((req,res) => {
    Product.find({})
    .sort({'_id':-1})
    .limit(10)
    .populate('ProductCatalog catalogName')
    .populate('Brand','brandName brandDescription')
    .then((data) => {
        if (data) {
            res.json({
                status: '200',
                msg: '',
                result: data
            })
        } else {
            res.json({
                status: '0',
                msg: '没有product',
                result: ''
            })
        }
    })
})

module.exports = productRouter

问题描述：
product 表关联查询 ProductCatalog Brand 两张表，两张表中只查询显示 catalogName brandName，但实际情况是查询并显示关联两张表的 id ，需要的字段内容没有显示出来。

{
"status": "200",
"msg": "",
"result": [
{
"_id": "60e134503b6ff901bc7c4114",
"productName": "水杯",
"productCatalog": "60d0aa16183981825073b21e",
"productMainPicture": "",
"productTotal": 88,
"productPrice": 77,
"productSalesTotal": 99,
"productStatus": false,
"productOrigin": "上海",
"brandName": "60e123a2b13e944620a9e2b4",
"createdAt": "2021-07-04T04:08:48.359Z",
"__v": 0
},
{
"_id": "60e1306d8c70524a88fd469f",
"productName": "萝卜干",
"productCatalog": "60d0a7fc3c322069dcfd007d",
"productMainPicture": "",
"productTotal": 55,
"productPrice": 44,
"productSalesTotal": 66,
"productStatus": true,
"productOrigin": "安徽",
"brandName": "60e1242cb13e944620a9e2b5",
"createdAt": "2021-07-04T03:52:13.223Z",
"__v": 0
},

]
}

我记得之前可以用 .populate('Model 查询字段') 这种方法查询的，但是不知道为什么现在不可以了，求指点，非常感谢！