MongoDB ObjectId与字符串ID比较返回false问题排查

我基于Node.js + MongoDB开发API，需要验证请求体中传入的字符串格式proposerId是否等于MongoDB查询返回的活动组织者ID（eventData.organizer._id是ObjectId类型）。日志显示两者ID值完全相同，但比较结果始终为false。

请求体内容 #

{    
    "participantId": "6238a608170aff10d16ccd89",    
    "proposerId": "62385d8caee17d13a1762b39", // this guy id is also an organizer    
    "gender": "female",    
    "groupId": "623aea21fcfad83bcf8d5bc4"
}

控制器验证代码 #

exports.addParticipantToEvent = async (req, res, next) => {  
  // Group Organizer constants  
  const eventId = req.params.eventId;  
  const groupId = req.body.groupId;  
  const proposerId = req.body.proposerId; // it can be an admin adding someone to the participants list  
  // Participant constants  
  const participantId = req.body.participantId;  
  const gender = req.body.gender;  

  // EVENT  
  // Does the event even exist?  
  const eventData = await Event.findById(eventId);  
  if (!eventData) {  
    return res.status(406).json({  
      code: 'EVENT_DOESNT_EXIST',  
      message: 'The event is not valid.',  
    });  
  }  
  console.log(eventData);  

  // What kind of users can participate in this event?  
  const allowedParticipants = eventData.allowedParticipants;  

  // whos the event organizer?  
  const eventOrganizer = eventData.organizer._id;  
  console.log('Organizer: ' + eventOrganizer);  
  console.log('Proposer: ' + proposerId);  
  console.log('Result: ' + proposerId === eventOrganizer);  

  try {  
    return res.status(200).json({  
      message: 'The participant can be added',  
      participantId: participantId,  
      gender: gender,  
      allowedParticipants: allowedParticipants,  
    });  
  } catch (err) {  
    return res.status(400).json({ message: err });  
  }
};

日志输出 #

{  
  location: { province: 'Barcelona' },  
  _id: new ObjectId("634ffee75990124926431e6f"),  
  title: 'Test open close 14',  
  sport: new ObjectId("622ce6ca672c3d4447676705"),  
  group: new ObjectId("623aea21fcfad83bcf8d5bc4"),  
  organizer: new ObjectId("62385d8caee17d13a1762b39"),  
  participants: [ new ObjectId("62385d8caee17d13a1762b39") ],  
  replacements: [],  
  invitations: [],  
  when: 2022-10-09T13:43:02.999Z,  
  open: true,  
  costPerParticipant: 4.4,  
  skill: 'novice',  
  allowedGender: 'female',  
  minParticipants: 2,  
  maxParticipants: 5,  
  visible: false,  
  externalLink: 'https://www.komoot.es/tour/731122050?ref=wta',  
  allowInvitations: true,  
  allowReplacements: false,  
  allowedParticipants: 'only-members',  
  createdAt: 2022-10-19T13:43:03.006Z,  
  updatedAt: 2022-10-19T13:43:03.006Z,  
  __v: 0  
}
Organizer: 62385d8caee17d13a1762b39
Proposer: 62385d8caee17d13a1762b39
false

解决方法 #

1. 修正运算符优先级问题 #

当前代码中console.log('Result: ' + proposerId === eventOrganizer)存在优先级错误：字符串拼接+的优先级高于全等运算符===，实际执行的是('Result: ' + proposerId) === eventOrganizer，必然返回false。必须给比较表达式加括号：

console.log('Result: ' + (proposerId === eventOrganizer.toString()));

2. 转换ObjectId为字符串后比较 #

将MongoDB返回的ObjectId通过toString()方法转为字符串，再和请求体的字符串ID比较：

const isMatch = proposerId === eventOrganizer.toString();
console.log('Result: ' + isMatch);

3. 使用ObjectId自带的equals()方法 #

MongoDB的ObjectId实例提供了equals()方法，可直接接收字符串或另一个ObjectId进行匹配判断：

const isMatch = eventOrganizer.equals(proposerId);
console.log('Result: ' + isMatch);

4. 查询时直接获取字符串ID（优化方案） #

如果后续不需要使用ObjectId类型，可以在查询时使用.lean()返回普通JS对象，此时_id会自动转为字符串：

const eventData = await Event.findById(eventId).lean();
const eventOrganizer = eventData.organizer._id; // 此时已为字符串类型
const isMatch = proposerId === eventOrganizer;

内容的提问来源于stack exchange，提问作者Minide