nodejs使用connect-mongodb报错（Please ensure that you set the default write concern）

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原本是使用connect-mongo的，可能是express版本的升级报错了，改用connect-mongodb，但是使用后出现了如下的警告：

G:\nodejs\moviesite>gruntRunning "concurrent:tasks" (concurrent) task    Running "nodemon:dev" (nodemon) task    Running "watch" task    Waiting...    [nodemon] v1.3.7    [nodemon] to restart at any time, enter `rs`    [nodemon] watching: *.*    [nodemon] starting `node app.js`    ========================================================================================    =  Please ensure that you set the default write concern for the database bysetting    =    =   one of the options           =    =           =    =     w: (value of > -1 or the string 'majority'), where < 1 means           =    =        no write acknowledgement            =    =     journal: true/false, wait for flush to journal before acknowledgement            =    =     fsync: true/false, wait for flush to file system before acknowledgement           =    =           =    =  For backward compatibility safe is still supported and           =    =   allows values of [true | false | {j:true} | {w:n, wtimeout:n} | {fsync:true}]      =    =   the default value is false which means the driver receives does not           =    =   return the information of the success/error of the insert/update/remove           =    =           =    =   ex: new Db(new Server('localhost', 27017), {safe:false})           =    =           =    =   http://www.mongodb.org/display/DOCS/getLastError+Command           =    =           =    =  The default of no acknowledgement will change in the very near future            =    =           =    =  This message will disappear when the default safe is set on the driver Db           =    ========================================================================================Sat, 27 Jun 2015 12:49:12 GMT express-session deprecated undefined resave option; provide resave option at app.js:20:9Sat, 27 Jun 2015 12:49:12 GMT express-session deprecated undefined saveUninitialized option; provide saveUninitialized option at app.js:20:9    moviesite started on port 3000

下边的警告在session中添加两个属性值restart和saveUninitialized即可解决。

Sat, 27 Jun 2015 12:49:12 GMT express-session deprecated undefined resave option; provide resave option at app.js:20:9Sat, 27 Jun 2015 12:49:12 GMT express-session deprecated undefined saveUninitialized option; provide saveUninitialized option at app.js:20:9如：    app.use(session({    resave: false,//重新保存：强制会话保存即使是未修改的。(默认值ture)    saveUninitialized: true,//强制保存未初始化的会话到存储器    cookie: {maxAge:3600000},     secret:'imooc',    store:new mongoStore({        url:dbUrl,        collection:'sessions'    })    }))

剩下的警告应该是数据库不是安全连接，还未能解决，知道的朋友告诉一下