windows下运行的nodejs。数据库mongodb安装并启动成功了。但在打开数据库mongodb.open(function(err, db) 时db总是undefined，err为{ [MongoError: connect UNKNOWN] name: 'MongoError', message: 'connect UNKNOWN' }。几天了也没有找到原因，还请大侠指教啊。
This error is returned for several errors like :
server is not running
you need to authenticate user
this database does not exists
the mongodb port is not the default port