使用Mongodb：TypeError：無法讀取未定義的屬性“集合”

Question

執行https://www.freecodecamp.com/challenges/store-data-in-mongodb時遇到此問題

錯誤消息原為

swyx:~/workspace $ learnyoumongo run find.js
/home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/node_modules/mongodb/lib/server.js:231
        process.nextTick(function() { throw err; })
                                      ^

TypeError: Cannot read property 'collection' of undefined
    at Exercise.<anonymous> (/home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/exercises/find/exercise.js:37:5)
    at next (/home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/node_modules/workshopper-exercise/exercise.js:271:17)
    at Exercise.end (/home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/node_modules/workshopper-exercise/exercise.js:277:5)
    at Workshopper.end (/home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/node_modules/workshopper/workshopper.js:191:12)
    at Workshopper.done (/home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/node_modules/workshopper/workshopper.js:323:19)
    at Exercise.<anonymous> (/home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/node_modules/workshopper-exercise/exercise.js:160:14)
    at /home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/node_modules/workshopper-exercise/exercise.js:147:16
    at /home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/exercises/find/exercise.js:20:21
    at /home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/node_modules/mongodb/lib/mongo_client.js:238:20
    at /home/ubuntu/.nvm/versions/node/v4.6.1/lib/node_modules/learnyoumongo/node_modules/mongodb/lib/db.js:242:14

這里還有其他類似的問題，但是沒有一個人描述這個確切的問題

供參考，這是我在其上運行的（有效）代碼

var mongo = require('mongodb').MongoClient
var age = process.argv[2]

var url = 'mongodb://localhost:27017/learnyoumongo'

mongo.connect(url, function(err, db) {
  if (err) throw err
  var parrots = db.collection('parrots')
  parrots.find({
    age: {
      $gt: +age
    }
  }).toArray(function(err, docs) {
    if (err) throw err
    console.log(docs)
    db.close()
  })
})

Answer 1

解決方案是我的mongodb服務器在一夜之間意外關閉，甚至沒有運行。 要重新啟動它，您必須恢復（ https://docs.mongodb.com/manual/tutorial/recover-data-following-unexpected-shutdown/ ），然后重新啟動。

Answer 2

在MongoDB本機NodeJS驅動程序的2.x版中，您將獲得數據庫對象作為connect回調的參數：

mongo.connect(url, (err, db) => {
  // Database returned
});

但是根據3.0的更改日志，您現在將獲得一個包含數據庫對象的客戶端對象：

mongo.connect(url, (err, client) => {
  // Client returned
  var db = client.db('mytestingdb');
});

close（）方法也已移至客戶端，因此您必須編寫client.close(); 代替db.close()