使用express框架时，用MongoDB存放session时，出现错误如下：

D:\WorkSpace\nodejs\user\node_modules\connect-mongo\lib\connect-mongo.js:153          throw new Error('Error connecting to database');                ^Error: Error connecting to database    at D:\WorkSpace\nodejs\user\node_modules\connect-mongo\lib\connect-mongo.js:153:17    at D:\WorkSpace\nodejs\user\node_modules\connect-mongo\node_modules\mongodb\lib\mongodb\db.js:229:16    at null.<anonymous> (D:\WorkSpace\nodejs\user\node_modules\connect-mongo\node_modules\mongodb\lib\mongodb\connection\server.js:578:7)    at EventEmitter.emit (events.js:106:17)    at null.<anonymous> (D:\WorkSpace\nodejs\user\node_modules\connect-mongo\node_modules\mongodb\lib\mongodb\connection\connection_pool.js:139:15)    at EventEmitter.emit (events.js:98:17)    at Socket.<anonymous> (D:\WorkSpace\nodejs\user\node_modules\connect-mongo\node_modules\mongodb\lib\mongodb\connection\connection.js:475:10)    at Socket.EventEmitter.emit (events.js:95:17)    at net.js:441:14    at process._tickCallback (node.js:415:13)

解决方法如下：

(数据库不带用户和密码的方法)

将  store: new MongoStore({db:settings.db})

替换成     store: new MongoStore({host:settings.host, port:settings.port, db:settings.db)})

在开始加上  format = require('util').format

app.use(express.session({

    secret: settings.cookieSecret,    key: settings.db,    cookie: {maxAge: 1000 * 60 * 30},//30 minute    store: new MongoStore({host:settings.host, port:settings.port, db:settings.db)})    /*store: new MongoStore({db:settings.db})*/}));

(数据库带用户和密码的方法)

将  store: new MongoStore({db:settings.db})

替换成     store: new MongoStore({url:format("mongodb://%s:%s@%s:%s/%s",settings.uid, settings.pwd, settings.host, settings.port, settings.db)})

在开始加上  format = require('util').format

app.use(express.session({

    secret: settings.cookieSecret,    key: settings.db,    cookie: {maxAge: 1000 * 60 * 30},//30 minute    store: new MongoStore({url:format("mongodb://%s:%s@%s:%s/%s",settings.uid, settings.pwd, settings.host, settings.port, settings.db)})    /*store: new MongoStore({db:settings.db})*/}));