下面是node app.js时的错误，这个看上去是mongodb的错，但是具体是什么错呢
path.exists is now called fs.exists.
NodeClub listening on port 3000 in development mode
God bless love....
You can debug your app with http://localhost:3000
/var/www/html/nodeclub/node_modules/mongoose/lib/utils.js:413 throw err; ^ TypeError: Uncaught, unspecified "error" event. at TypeError () at NativeConnection.EventEmitter.emit (events.js:74:15) at /var/www/html/nodeclub/node_modules/mongoose/lib/model.js:561:31 at /var/www/html/nodeclub/node_modules/mongoose/lib/utils.js:408:16 at /var/www/html/nodeclub/node_modules/mongoose/node_modules/mongodb/lib/mongodb/db.js:1160:28 at /var/www/html/nodeclub/node_modules/mongoose/node_modules/mongodb/lib/mongodb/db.js:1301:30 at /var/www/html/nodeclub/node_modules/mongoose/node_modules/mongodb/lib/mongodb/cursor.js:144:30 at /var/www/html/nodeclub/node_modules/mongoose/node_modules/mongodb/lib/mongodb/cursor.js:186:32 at /var/www/html/nodeclub/node_modules/mongoose/node_modules/mongodb/lib/mongodb/cursor.js:498:39 at Cursor.close (/var/www/html/nodeclub/node_modules/mongoose/node_modules/mongodb/lib/mongodb/cursor.js:782:5)