TypeError：无法读取未定义节点js的属性'_id'答案

【问题标题】：TypeError: Cannot read property '_id' of undefined node jsTypeError：无法读取未定义节点js的属性'_id'
【发布时间】：2017-03-12 07:07:01
【问题描述】：

我正在关注 Adam Bretz 和 Colin J. Ihrig 的 FULL Stack JAVASCRIPT DEVELOPMENT WITH MEAN。当我进入第 8 章时，尝试插入在线 mongo 数据库时无法克服这个错误。我需要使用旧版本的节点吗？我查看了堆栈交换，但无法在所有建议的修复后使其工作...... 这是我的错误：

TypeError: Cannot read property '_id' of undefined
    at insertEmployees (/Users/kikocarisse/Desktop/NODESITES/chapter8/index.js:100:17)
    at /Users/kikocarisse/Desktop/NODESITES/chapter8/index.js:195:5
    at /Users/kikocarisse/Desktop/NODESITES/chapter8/index.js:79:7
    at Function.<anonymous> (/Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/lib/model.js:3369:16)
    at /Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/lib/model.js:1890:18
    at /Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/node_modules/async/internal/parallel.js:35:9
    at /Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/node_modules/async/node_modules/lodash/before.js:31:21
    at iteratorCallback (/Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/node_modules/async/eachOf.js:52:13)
    at /Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/node_modules/async/internal/onlyOnce.js:12:16
    at /Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/node_modules/async/internal/parallel.js:32:13
    at apply (/Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/node_modules/async/node_modules/lodash/_apply.js:15:25)
    at /Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/node_modules/async/node_modules/lodash/_overRest.js:32:12
    at model.callbackWrapper (/Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/lib/model.js:1865:11)
    at next_ (/Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/node_modules/hooks-fixed/hooks.js:89:34)
    at fnWrapper (/Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/node_modules/hooks-fixed/hooks.js:186:8)
    at /Users/kikocarisse/Desktop/NODESITES/chapter8/node_modules/mongoose/lib/model.js:3369:16

这是我的代码：

"use strict";
var a = require('./a.js');
var b = new a(5);
var mongoose = require('./node_modules/mongoose');
var express = require('express');
var app = express();

var bodyParser = require('./node_modules/body-parser');
app.use(bodyParser.urlencoded({
  extended: true
}));
app.route('/echo')
    .all((req,res)=>{
        let pars = (Object.keys(req.body).length > 0)?req.body:req.query;
        res.send(pars);
    });


var Schema = mongoose.Schema;
var db = mongoose.connection;
var dbUrl = 'mongodb://*****:******@******:*****/****';

var TeamSchema = new Schema({
  name: {
    type: String,
    required: true
  }
});
var Team = mongoose.model('Team', TeamSchema);

var EmployeeSchema = new Schema({
  name: {
    first: {
      type: String,
      required: true
    },
    last: {
      type: String,
      required: true
    }
  },
  team: {
    type: Schema.Types.ObjectId,
    ref: 'Team'
  },
  image: {
    type: String,
    default: 'images/user.png'
  },
  address: {
    lines: {
      type: [String]
    },
    postal: {
      type: String
    }
  }
});

var Employee = mongoose.model('Employee', EmployeeSchema);


db.on('error', function () {
  console.log('there was an error communicating with the database');
});

function insertTeams (callback) {
  Team.create([{
    name: 'Product Development'
  }, {
    name: 'Dev Ops'
  }, {
    name: 'Accounting'
  }], function (error, pd, devops, acct) {
    if (error) {
      return callback(error);
    } else {
      console.info('teams successfully added')
      callback(null, pd, devops, acct);
    }
  });
}

function insertEmployees (pd, devops, acct, callback) {
  Employee.create([{
    name: {
      first: 'John',
      last: 'Adams'
    },
    team: pd._id,
    address: {
      lines: ['2 Lincoln Memorial Cir NW'],
      postal: '20037'
    }
  }, {
    name: {
      first: 'Thomas',
      last: 'Jefferson'
    },
    team: devops._id,
    address: {
      lines: ['1600 Pennsylvania Avenue', 'White House'],
      postal: '20500'
    }
  }, {
    name: {
      first: 'James',
      last: 'Madison'
    },
    team: acct._id,
    address: {
      lines: ['2 15th St NW', 'PO Box 8675309'],
      postal: '20007'
    }
  }, {
    name: {
      first: 'James',
      last: 'Monroe'
    },
    team: acct._id,
    address: {
      lines: ['1850 West Basin Dr SW', 'Suite 210'],
      postal: '20242'
    }
  }], function (error, johnadams) {
    if (error) {
      return callback(error);
    } else {
      console.info('employees successfully added');
      callback(null, {
        team: pd,
        employee: johnadams
      });
    }
  })
}

function retrieveEmployee (data, callback) {
  Employee.findOne({
    _id: data.employee._id
  }).populate('team').exec(function (error, result) {
    if (error) {
      return callback (error);
    } else {
      console.log('*** Single Employee Result ***');
      console.dir(result);
      callback(null, data);
    }
  });
}

function retrieveEmployees (data, callback) {
  Employee.find({
    'name.first': /J/i
  }, function (error, results) {
    if (error) {
      return callback(error);
    } else {
      console.log('*** Multiple Employees Result ***')
      console.dir(results);
      callback(null, data);
    }
  });
}

function updateEmployee (first, last, data, callback) {
  console.log('*** Changing names ***');
  console.dir(data.employee);

  var employee = data.employee;
  employee.name.first = first;
  employee.name.last = last

  employee.save(function (error, result) {
    if (error) {
      return callback(error);
    } else {
      console.log('*** Changed name to Andrew Jackson ***');
      console.log(result);
      callback(null, data);
    }
  });
}

mongoose.connect(dbUrl, function (err) {
  if (err) {
    return console.log('there was a problem connecting to the database!' + err);
  }
  console.log('connected!');

  insertTeams(function (err, pd, devops, acct) {
    if (err) {
      return console.log(err)
    }
    insertEmployees(pd, devops, acct, function (err, result) {

      retrieveEmployee(result, function (err, result) {

        retrieveEmployees(result, function (err, result) {

          updateEmployee('Andrew', 'Jackson', result, function (err, result) {
            if (err) {
              console.error(err);
            } else {
              console.info('database activity complete')
            }

            db.close();
            process.exit();
          });
        });
      });
    });
  });
});

【问题讨论】：

以后调试用； 1.查看错误消息的堆栈跟踪文件和行号； 2. 导航到该行的第一个文件； 3. 如果您的标识符紧接在它之前，则记录所有； 4. 如果出现意外情况，要么添加逻辑以将其捕获，要么返回堆栈跟踪的一级并重复

标签： javascript node.js mongodb mongoose

【解决方案1】：

在第 100 行，devops 变量是 undefined，这就是您收到错误的原因。请参阅insertTeams 函数，这是您在创建团队时首先获得 devops 价值的地方。

这可能就是为什么你的创建回调是这样的：function (error, pd, devops, acct) 但看到Mongoose docs，它传递一个数组作为创建的第二个参数。

试试这个：

function insertTeams (callback) {
  Team.create([{
    name: 'Product Development'
  }, {
    name: 'Dev Ops'
  }, {
    name: 'Accounting'
  }], function (error, teams) {
    if (error) {
      console.log(error);
      return callback(error);
    } else {
      console.info('teams successfully added')
      callback(null, teams[0], teams[1], teams[2]);
    }
  });
}

请注意，现在它获取了一个数组并将其元素传递给回调，还请注意我添加了一个日志，如果有错误，您可以看到它发生的位置。

此外，如果您阅读错误日志并指出错误发生的行内容是什么，这会有所帮助，请注意我们这里没有行号，这使得查找错误更加困难。

【讨论】：