MongoDB App Services自定义用户元数据出现EJSON.parse错误排查

我正在MongoDB App Services中构建用户注册触发的创建函数，数据库的UserSchema如下：

{
  "title": "UserSchema",
  "properties": {
    "_id": {
      "bsonType": "objectId"
    },
    "user_id": {
      "bsonType": "string"
    },
    "username": {
      "bsonType": "string"
    },
    "email": {
      "bsonType": "string"
    },
    "password": {
      "bsonType": "string"
    },
    "profilePic": {
      "bsonType": "string"
    },
    "createdAt": {
      "bsonType": "date"
    },
    "followers": {
      "bsonType": "array",
      "items": {
        "bsonType": "string"
      }
    },
    "following": {
      "bsonType": "array",
      "items": {
        "bsonType": "string"
      }
    },
    "cardsInCollection": {
      "bsonType": "array",
      "items": {
        "bsonType": "string"
      }
    }
  },
  "required": [
    "_id",
    "user_id",
    "username",
    "email",
    "password",
    "profilePic",
    "createdAt"
  ]
}

编写的函数代码：

exports = async function onUserCreation(user) {
  const customUserDataCollection = context.services
    .get("service") // 此处已正确填写服务名
    .db("app") // 此处已正确填写数据库名
    .collection("users"); 
  try {
    await customUserDataCollection.insertOne({
      user_id: user.id,
      username:user.username,
      email: user.email,
      password: user.password,
      profilePic: user.profilePic,
      createdAt: user.createdAt,
      followers: user.following,
      following: user.followers,
      cardsInCollection: user.cardsInCollection,
    });
  } catch (e) {
    console.error(`Failed to create custom user data document for user:${user.id}`);
    throw e
  }
}

测试控制台输入：

exports({
  id: "1234567890abcdef12345678",
  username: "someusername",
  email: "someemail@email",
  password: "password",
  profilePic: "yes",
  createdAt: Date.parse("2023-07-28T22:38:14.415+00:00"),
  followers: [],
  following: [],
  cardsInCollection: [],
})

返回结果：

> took 148.904629ms
> result: 
{
  "$undefined": true
}
> result (JavaScript): 
EJSON.parse('{"$undefined":true}')

请问哪里出错了？该如何修复？

问题分析与修复方案 #

1. 函数无返回值导致$undefined结果 #

你的异步函数没有任何返回语句，MongoDB App Services执行后会返回undefined，在EJSON中被序列化为{"$undefined": true}，这是测试结果显示该内容的直接原因。

2. 字段赋值错误 #

函数中把followers和following的赋值搞反了：

followers: user.following,
following: user.followers,

需要修正为：

followers: user.followers,
following: user.following,

3. createdAt类型不匹配 #

测试输入中用Date.parse()得到的是时间戳（数字类型），但Schema要求date类型，需要转换为Date对象：

createdAt: new Date("2023-07-28T22:38:14.415+00:00"),

4. 可选字段默认值处理 #

如果注册时用户未提供followers、following、cardsInCollection，建议设置默认空数组，保证文档结构一致性（虽然Schema中它们不是必填项）。

修复后的完整代码 #

exports = async function onUserCreation(user) {
  const customUserDataCollection = context.services
    .get("service") // 确保此处是你的实际服务名称
    .db("app") // 确保此处是你的实际数据库名称
    .collection("users"); 
  try {
    const insertResult = await customUserDataCollection.insertOne({
      user_id: user.id,
      username: user.username,
      email: user.email,
      password: user.password,
      profilePic: user.profilePic,
      createdAt: typeof user.createdAt === 'number' ? new Date(user.createdAt) : user.createdAt,
      followers: user.followers || [],
      following: user.following || [],
      cardsInCollection: user.cardsInCollection || [],
    });
    // 返回插入结果，方便测试验证
    return insertResult;
  } catch (e) {
    console.error(`Failed to create custom user data document for user:${user.id}`);
    throw e;
  }
}

修复后的测试输入 #

exports({
  id: "1234567890abcdef12345678",
  username: "someusername",
  email: "someemail@email",
  password: "password",
  profilePic: "yes",
  createdAt: new Date("2023-07-28T22:38:14.415+00:00"),
  followers: [],
  following: [],
  cardsInCollection: [],
})

修改后测试会返回插入操作的结果（如insertedId等信息），同时解决了字段赋值错误和类型不匹配的问题。

内容的提问来源于stack exchange，提问作者Darius