Mongoose自引用模型中populate()方法无效问题排查

我确认代码中已调用populate()方法（传入错误路径会报错），但该方法似乎未产生任何效果。我在Stack Overflow搜索后未找到自引用模型相关案例，因此怀疑问题出在自引用上。我参考了Mongoose官方文档学习populate()的用法。

我的模型 #

const mongoose = require('mongoose');

const schema = new mongoose.Schema({
    firstName: { type: String },
    lastName: { type: String },
    email: { type: String, unique: true },
    teamLeaders: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Agent' }],
    teamMembers: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Agent' }]
});

let Agent = mongoose.model('Agent', schema);
Agent.init();

module.exports = Agent;

MongoDB Atlas中的实际文档（已匿名化姓名和邮箱） #

{
  "_id": {
    "$oid": "62e3e0ab57560a5c15a535e0"
  },
  "teamLeaders": [],
  "teamMembers": [
    {
      "$oid": "62e3f548678dbed5593acc8e"
    },
    {
      "$oid": "62e3f548678dbed5593acc91"
    },
    {
      "$oid": "62e3f548678dbed5593acc94"
    },
    {
      "$oid": "62e3f548678dbed5593acc97"
    },
    {
      "$oid": "62e3f548678dbed5593acc9a"
    },
    {
      "$oid": "62e3f548678dbed5593acc9d"
    },
    {
      "$oid": "62e3f548678dbed5593acca0"
    },
    {
      "$oid": "62e3f548678dbed5593acca3"
    }
  ],
  "firstName": "John",
  "lastName": "Smith",
  "email": "john@smith.com",
  "__v": 8
}

调用populate()的代码 #

const Agent = require('../models/agents');

const mongoose = require("mongoose");
const db = require("../config/db");
mongoose.connect(process.env.MONGODB_URI || db.url);

// 已移除无关函数，数据库连接正常

// 代码中的实际私有函数
async function addAgent(firstName, lastName, email, isTeamLeader, teamLeader) {
    let newAgent = Agent();

    newAgent.firstName = firstName;
    newAgent.lastName = lastName;
    newAgent.email = email;

    if (isTeamLeader) {
        await newAgent.save();
    } else {
        newAgent.teamLeaders.push(teamLeader);

        let savedAgent = await newAgent.save();

        teamLeader.teamMembers.push(savedAgent);
        await teamLeader.save();
    }
}

// 用于展示创建代理方式的示例函数
async function createAgents() {
    await addAgent('John', 'Smith', 'john@smith.com', true, null);

    // 稍后手动调用addAgent()，因团队仅30人
    // 因此仅通过firstName查询，团队内仅有一个John
    let teamLeader = await Agent.findOne({ firstName: 'John' });
    await addAgent('Peter', 'Parker', 'peter@parker.com', false, teamLeader);
}

// 调用populate()的核心函数
async function mainFunction() {
    Agent.findOne({ firstName: 'John' }).populate({ path: 'teamMembers', model: 'Agent' }).exec((err, agent) => {
        if (err) return handleError(err);
        console.log('Populated agent: ' + agent);
    });
}

内容的提问来源于stack exchange，提问作者jon2512chua