Node + MongoDB – 连接池 – mongoldb-native

我试图实现一个优雅的代码，以解决与mongoldb本地节点的连接池。 但是，我没有成功为此做一个模块。 我肯定这是关于提升的事情，但我无法得到它。

Mongodb.js

'use strict'; var client = require('mongodb').MongoClient; var connectionString = undefined; var db = undefined; switch(process.env.NODE_ENV) { case 'production': connectionString = process.env.MONGOLAB_URI; break; case 'test': connectionString = 'mongodb://localhost:27017/test'; break; default: connectionString = 'mongodb://localhost:27017/development'; } client.connect(connectionString, function(err, database) { if (err) throw err; console.log('MongoDB running on ' + (process.env.NODE_ENV || 'development') + ' environment'); database.on('error', function(err) { throw err; }); db = database; }); module.exports = db; 

App.js

 var express = require('express'); var app = express(); var db = require('./lib/mongodb'); var professional = require('./routes/professional'); app.use('/professional', professional); db.listCollections().toArray() .then(function(items) { console.log(items); }); module.exports = app; 

安慰

 Julios-MacBook-Air:klou juliocoelho$ ./bin/www /Users/juliocoelho/Projects/klou/app.js:10 db.listCollections().toArray() ^ TypeError: Cannot read property 'listCollections' of undefined at Object.<anonymous> (/Users/juliocoelho/Projects/klou/app.js:10:3) at Module._compile (module.js:435:26) at Object.Module._extensions..js (module.js:442:10) at Module.load (module.js:356:32) at Function.Module._load (module.js:311:12) at Module.require (module.js:366:17) at require (module.js:385:17) at Object.<anonymous> (/Users/juliocoelho/Projects/klou/bin/www:3:11) at Module._compile (module.js:435:26) at Object.Module._extensions..js (module.js:442:10) 

Answer 1

由于node.js的asynchronous特性，您需要导出callback分配方法来获取variables，并在asynchronous执行时调用它。 以下代码更好地解释了它：

 'use strict'; var client = require('mongodb').MongoClient; var connectionString = undefined; var db, callback; switch(process.env.NODE_ENV) { case 'production': connectionString = process.env.MONGOLAB_URI; break; case 'test': connectionString = 'mongodb://localhost:27017/test'; break; default: connectionString = 'mongodb://localhost:27017/development'; } client.connect(connectionString, function(err, database) { if (err) throw err; console.log('MongoDB running on ' + (process.env.NODE_ENV || 'development') + ' environment'); database.on('error', function(err) { throw err; }); db = database; if( typeof callback == 'function' ){ callback(db); } }); module.exports = function(cb){ if(typeof db != 'undefined'){ cb(foo); // If db is already defined, don't wait. } else { callback = cb; } } 

App.js

 var dbModule = require('./lib/mongodb'); dbModule(function(db){ //Here code using db; db.listCollections() .toArray() .then(function(items) { console.log(items); }); });