TypeError：无法读取未定义的属性“toString” - 为什么？

Question

这是发生这种情况的第 (50) 行：

var meetingId = meeting._id.toString(),

这是完整的相关代码：

var MongoClient = require('mongodb').MongoClient;
var assert = require('assert');
var ObjectId = require('mongodb').ObjectID;
var config = require('./config'),
    xlsx = require('./xlsx'),
    utils = require('./utils'),
    _ = require('lodash'),
    url = config.DB_URL;

var meetings = [];

function findNumberOfNotesByMeeting(db, meeting, callback) {
    var meetingId = meeting._id.toString(),
        meetingName = meeting.name.displayValue,
        attendees = meeting.attendees;
        host = meeting.host;

    var count = 1, pending = 0, accepted = 0;
    console.log("==== Meeting: " + meetingName + '====');
    _.each(attendees, function(item) {
      console.log(count++ + ': ' + item.email + ' (' + item.invitationStatus + ')');
      if (item.invitationStatus == 'pending') { pending++; }
      else if (item.invitationStatus == 'accepted') { accepted++; }
    });
    console.log("*** " + attendees.length + ", " + pending + "," + accepted);

    db.collection('users').findOne({'_id': new ObjectId(host)}, function(err, doc) {
        var emails = [];
        if (doc.emails) {
            doc.emails.forEach(function(e) {
                emails.push(e.email + (e.primary ? '(P)' : ''));
            });
        }
        var email = emails.join(', ');
        if (utils.toSkipEmail(email)) {
            callback();
        } else {
            db.collection('notes').find({ 'meetingId': meetingId }).count(function(err, count) {
                if (count != 0) {
                    console.log(meetingName + ': ' + count + ',' + attendees.length + ' (' + email + ')');
                    meetings.push([ meetingName, count, email, attendees.length, pending, accepted ]);
                }
                callback();
            });
        }
    });
}

function findMeetings(db, meeting, callback) {  
    var meetingId = meeting._id.toString(),
        host = meeting.host;
    db.collection('users').findOne({'_id': new ObjectId(host)}, function(err, doc) {
        var emails = [];
        if (!err && doc && doc.emails) {
            doc.emails.forEach(function(e) {
                emails.push(e.email + (e.primary ? '(P)' : ''));
            });
        }

        var email = emails.join(', ');

        if (utils.toSkipEmail(email)) {
            callback();
        } else {
            db.collection('notes').find({ 'meetingId': meetingId }).count(function(err, count) {
                if (count != 0) {
                    var cursor = db.collection('meetings').find({
                    'email': {'$regex': 'agu', '$options': 'i' }
                    });
                }
                callback();
        }); 

        }   


    cursor.count(function(err, count) {
        console.log('count: ' + count);
        var cnt = 0;
        cursor.each(function(err, doc) {
            assert.equal(err, null);
            if (doc != null) {
                findNumberOfNotesByMeeting(db, doc, function() {
                    cnt++;
                    if (cnt >= count) { callback(); }
                });
            }
        });
    });
    });
}


MongoClient.connect(url, function(err, db) {
    assert.equal(null, err);
    findMeetings(db, function() {
        var newMeetings = meetings.sort(function(m1, m2) { return m2[1] - m1[1]; });
        newMeetings.splice(0, 0, [ 'Meeting Name', 'Number of Notes', 'Emails' ]);
        xlsx.writeXLSX(newMeetings, config.xlsxFileNameMeetings);
        db.close();
    });
});

如您所见，会议变量（我几乎 100% 肯定是问题所在，而不是 _id 属性）作为参数传入之前的函数 findNumberOfNotesByMeeting。我在这里找到了一些关于我的新函数可能是异步的并且需要回调这一事实的信息，但我试图这样做并且不确定如何让它工作，或者即使这是正确的修复为我的代码。

Answer 1

您没有将meeting 对象传递给findMeetings，它期望它作为第二个参数。该函数不是获取meeting 对象，而是在其位置接收回调函数，因此尝试执行meeting._id 是未定义的。

其实findMeetings函数的作用是什么？它的名称表明它可以找到数据库中的所有会议，或具有特定 ID 的所有会议。您在没有会议 ID 的情况下调用它，表明您可能正在尝试查找所有会议，但它的实现需要一个会议对象。您需要先清除它。