Question

我想通过mongoskin从mongodb中读取一些数据。但是当我尝试调用localhost：3000 / tasks

时，nodejs会抛出一个错误

在我的数据库'todo'中，集合'tasks'中有一些项目。当我启动应用程序时，控制台中的结果正常。

谁能看到我写错了什么？

eroor消息：

500 TypeError: Cannot read property 'tasks' of undefined
at exports.list (/Users/piet/Websites/privat/mongo/routes/tasks.js:7:8) at callbacks     (/Users/piet/Websites/privat/mongo/node_modules/express/lib/router/index.js:164:37)
at param (/Users/piet/Websites/privat/mongo/node_modules/express/lib/router/index.js:138:11)
at pass (/Users/piet/Websites/privat/mongo/node_modules/express/lib/router/index.js:145:5)
at Router._dispatch    (/Users/piet/Websites/privat/mongo/node_modules/express/lib/router/index.js:173:5)
at Object.router   (/Users/piet/Websites/privat/mongo/node_modules/express/lib/router/index.js:33:10)
at next   (/Users/piet/Websites/privat/mongo/node_modules/express/node_modules/connect/lib/proto.js:193:    15)
at Object.methodOverride [as handle]  (/Users/piet/Websites/privat/mongo/node_modules/express/node_modules/connect/lib/middleware/me    thodOverride.js:48:5)
at next (/Users/piet/Websites/privat/mongo/node_modules/express/node_modules/connect/lib/proto.js:193:    15)
at Object.urlencoded [as handle]   (/Users/piet/Websites/privat/mongo/node_modules/express/node_modules/connect/lib/middleware/ur    lencoded.js:49:37)

我的app.js：

var express = require('express');
var routes = require('./routes');
var tasks = require('./routes/tasks');
var http = require('http');
var path = require('path');

var mongo = require("mongoskin");
var db = mongo.db('localhost:27017/todo?auto_reconnect=true', { 
safe:true })
.collection('tasks')
.find()
.toArray(function(error, items){
    console.log(items);
})

var app = express();
app.set('port', process.env.PORT || 3000);
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');
app.use(express.favicon());
app.use(express.logger('dev'));
app.use(express.json());
app.use(express.urlencoded());
app.use(express.methodOverride());
app.use(app.router);
app.use(express.static(path.join(__dirname, 'public')));

if ('development' == app.get('env')) {
   app.use(express.errorHandler());
}
app.get('/', routes.index);
app.get('/tasks', tasks.list);
http.createServer(app).listen(app.get('port'), function(){
  console.log('Express server listening on port ' + app.get('port'));
});

/routes/tasks.js下的路径文件

exports.list = function(req, res, next){
req.db.tasks.find({
    completed: false
}).toArray(function(error, tasks){
    res.render('tasks', {
        title: "ToDo list",
        name: tasks = tasks || []
    })
})
};

Answer 1

使用28017作为端口ID。您可以在“req.db”中查看您的内容。 Mayb这是未定义的。

Answer 2

您将需要一个中间件来将收集对象与您的请求挂钩：

var db    = mongo.db('localhost:27017/todo?auto_reconnect=true');
var tasks = db.collection('tasks');
...
app.use(function(req, res, next) {
  req.db = { tasks : tasks }; // this exposes the collection as `req.db.tasks`
                              // to your route handlers
  next();
});
app.use(app.router);
...

Answer 3

在您的routes / task.js中，req是Express.js的请求对象。它没有“db”句柄，这就是你收到错误的原因：

500 TypeError: Cannot read property 'tasks' of undefined

在app.js中，这是获取db句柄的错误方法：

var mongo = require("mongoskin");
var db = mongo.db('localhost:27017/todo?auto_reconnect=true', { safe:true })
   .collection('tasks')
   .find()
   .toArray(function(error, items){
       console.log(items);
   });

db代码应该移动到一个单独的模块中（例如dbConnection.js），这样每次需要db句柄时，你只需要这样做：

var db = require('./dbConnection').getDb();

routes / task.js需要获取db句柄才能进行数据库调用。所以这里是你修改过的app.js，routes / task.js和新的dbConnection.js文件：

dbConnection.js：

var open = function() {
    return require('mongoskin').db('localhost:27017/todo?auto_reconnect=true',
        {safe: true, strict: false}
    );
};

var db = open();

var dbConnection = {
    getDb: function() {
        if (!db) {
           db = open();
        }
        return db;
    }
};

module.exports = dbConnection;

路由/ task.js：

var db = require('../dbConnection').getDb();

exports.list = function(req, res, next){
    var tasksCollection = db.collection('tasks');

    tasksCollection.find({ completed: false }).toArray(function(error, tasks){
        res.render('tasks', {
            title: "ToDo list",
            name: (tasks || [])
        });
    });
};

app.js：

var express = require('express');
var routes = require('./routes');
var tasks = require('./routes/tasks');
var http = require('http');
var path = require('path');

var app = express();
app.set('port', process.env.PORT || 3000);
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');
app.use(express.favicon());
app.use(express.logger('dev'));
app.use(express.json());
app.use(express.urlencoded());
app.use(express.methodOverride());
app.use(app.router);
app.use(express.static(path.join(__dirname, 'public')));

if ('development' == app.get('env')) {
    app.use(express.errorHandler());
}
app.get('/', routes.index);
app.get('/tasks', tasks.list);
http.createServer(app).listen(app.get('port'), function(){
    console.log('Express server listening on port ' + app.get('port'));
});

Mongoskin不会从nodejs app中的mongodb获取一些结果

3 个答案: