heroku上的Node.js和Mongo会话错误

将我的应用程序部署到heroku时出现以下错误。我在localhost上没有任何错误。我错过了什么

GET/304 522ms GET/public/stylesheets/bootstrap.css 200 15ms- 131.2kb GET/public/stylesheets/style.css 200 3ms-799b GET/public/images/food2.jpg 200 62ms-812.2kb /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/connection/base.js:242

     throw message;       
            ^    **Error: Error setting TTL index on collection : sessions**  at

/app/node_modules/connect mongo/lib/connect mongo.js:161:23 at /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/db.js:1404:28 在 /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/db.js:1542:30 在 /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/cursor.js:159:22 在 /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/cursor.js:685:39 在光标处。关闭 /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/cursor.js:959:5 在commandHandler /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/cursor.js:685:21 在 /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/db.js:1806:9 在Server.Base上。\u callHandler /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/connection/base.js:442:41 在 /app/node_modules/connect mongo/node_modules/mongodb/lib/mongodb/connection/server.js:485:18

github项目是

我也尝试过这段代码，但得到了相同的错误：

  app.use(session({
    secret: 'asdfghjkl',
    store: new MongoStore({
      db: 'app27253116',
      collection: 'sessions',
      host: 'kahana.mongohq.com',
      port: 10097
    }),
    cookie: {maxAge: 900000}
  }));

试试这个：

 store: new MongoStore({
      db: 'restaurants',
      collection: 'sessions',
      host: 'localhost',
      port: 27017,
      auto_reconnect:true
 }),

 store: new MongoStore({
      db: 'restaurants',
      collection: 'sessions',
      host: 'localhost',
      port: 27017,
      auto_reconnect:true
 }),