关于 Node.js 的问题。模式和模型

Question

关于 Node.js 的问题。架构、模型和 npm。 我是 node.js 的新手，正在按照步骤在 mongoose 文档中制作模式和模型。

http://mongoosejs.com/docs/

我正在尝试使用 kittens.js 输出我在 index.js 中制作的模型，但我不确定我是否正确。

编译时出错，

C:\Atom\initial\index.js:11
db.on('error', console.error.bind(console, 'connection_error'));
  ^

TypeError: Cannot read property 'on' of undefined
    at Object.<anonymous> (C:\Atom\initial\index.js:11:3)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.runMain (module.js:604:10)
    at run (bootstrap_node.js:394:7)
    at startup (bootstrap_node.js:149:9)
    at bootstrap_node.js:509:3

我在 index.js 中有以下代码。

    var express = require('express');
    var mongoose = require('mongoose');
    var path = require('path');
    var logger = require('morgan');
    var bodyParser = require('body-parser');
    var Kitty = require('./models/kittens.js');
    mongoose.connect("my database");

    db.on('error', console.error.bind(console, 'connection_error'));

    db.once('open', function(){
       console.log("Connected!");
    });

    var db = mongoose.connection;

    var Kitty = db.model('Kitty', kittySchema);

    var silence = new Kitty({name: 'Silence'});
    console.log(silence.name);

    db.close();

这是我的模型架构。

    var mongoose = require('mongoose');
    var Schema = mongoose.Schema;

    var kittySchema = new Schema({
     name: String
    });

    var Kitty = mongoose.model('Kitty', kittySchema);
    module.exports = Kitty;

一开始我以为是因为我没有安装 npm express 和 mongoose，但是当我尝试安装它们时，会出现这样的错误消息

[    ..............] \ fetchMetadata: verb afterAddevents.js:160ps://registry.npmjs.org/mime-types
      throw er; // Unhandled 'error' event
      ^

Error: This socket is closed
    at WriteStream.Socket._writeGeneric (net.js:678:19)
    at WriteStream.Socket._write (net.js:729:8)
    at doWrite (_stream_writable.js:333:12)
    at writeOrBuffer (_stream_writable.js:319:5)
    at WriteStream.Writable.write (_stream_writable.js:246:11)
    at WriteStream.Socket.write (net.js:656:40)
    at Object.Gauge._doRedraw (C:\Program Files\nodejs\node_modules\npm\node_modules\npmlog\node_mo
dules\gauge\index.js:208:26)
    at Object.Gauge.hide (C:\Program Files\nodejs\node_modules\npm\node_modules\npmlog\node_modules
\gauge\index.js:162:8)
    at EventEmitter.log.clearProgress (C:\Program Files\nodejs\node_modules\npm\node_modules\npmlog
\log.js:127:14)
    at EventEmitter.log.disableProgress (C:\Program Files\nodejs\node_modules\npm\node_modules\npml
og\log.js:88:8)

当我尝试在其他文件中安装 express 和 mongoose 时，也发生了这种情况。

任何想法都可以帮助我！谢谢！

Answer 1

实际上函数是在顶部提升的，所以首先你必须定义 db 变量然后使用它。

 var express = require('express');
    var mongoose = require('mongoose');
    var path = require('path');
    var logger = require('morgan');
    var bodyParser = require('body-parser');
    var Kitty = require('./models/kittens.js');
    mongoose.connect("my database");
    var db = mongoose.connection;

    db.on('error', console.error.bind(console, 'connection_error'));

    db.once('open', function(){
       console.log("Connected!");
    });



    var Kitty = db.model('Kitty', kittySchema);

    var silence = new Kitty({name: 'Silence'});
    console.log(silence.name);

    db.close();