Node.js 单连接到 MongoDB

connection.js:

var Db = require('mongodb').Db;
var Connection = require('mongodb').Connection;
var Server = require('mongodb').Server;
//the MongoDB connection
var connectionInstance; 
module.exports = function(callback) {
  //if already we have a connection, don't connect to database again
  if (connectionInstance) {
    callback(connectionInstance);
    return;
  } 
  var db = new Db('your-db', new Server("127.0.0.1", Connection.DEFAULT_PORT, { auto_reconnect: true }));
  db.open(function(error, databaseConnection) {
    if (error) throw new Error(error);
    connectionInstance = databaseConnection;
    callback(databaseConnection);
  });
};

使用的方法很简单：

var mongoDbConnection = require('./lib/connection.js'); 
exports.index = function(req, res, next) {
  mongoDbConnection(function(databaseConnection) {
    databaseConnection.collection('collectionName', function(error, collection) {
      collection.find().toArray(function(error, results) {
        //blah blah
      });
    });
  });
};

可从 Gist 上下载代码：
connection.js
example-connection.js