nodejs基础开发新建项目出throw new Error('Required MongoStore option `db` missing')

明明都是照着书来写，但是遇到版本的问题真的好多，一路百度过来。在这里卡住了。建立MongoDB数据库链接，老是报错。 package.json也配置了，models文件夹也建立。settings.js也有了。但是还是错。求高人指点...

D:\node\microblog\node_modules\connect-mongo\lib\connect-mongo.js:96 throw new Error('Required MongoStore option db missing'); ^ Error: Required MongoStore option db missing at new MongoStore (D:\node\microblog\node_modules\connect-mongo\lib\connect- mongo.js:96:15) at Object. (D:\node\microblog\app.js:33:12) at Module._compile (module.js:456:26) at Object.Module._extensions..js (module.js:474:10) at Module.load (module.js:356:32) at Function.Module._load (module.js:312:12) at Function.Module.runMain (module.js:497:10) at startup (node.js:119:16) at node.js:906:3