node.js - mongodb.connect不执行回调函数

Question

我正在尝试连接到我的 Mongodb 并插入一些文档(如果它们不在数据库中)。它在第一次插入时工作正常，但在函数 existInDatabase 中它有时不执行回调函数。

var MongoClient = require('mongodb').MongoClient;
var mongoData = require('./mongoData');
var exports = module.exports = {};
var dbName = 'checklist';

MongoClient.connect(mongoData.ConString, {
  useNewUrlParser: true
}, function(err, db) {
  if (err) throw err;
  for (var key in mongoData.Customers) {
    if (!existsInDatabase(mongoData.Customers[key], 'Customers')) {
      db.db(dbName).collection('Customers').insertOne(mongoData.Customers[key], function(err, res) {
        if (err) throw err;
        console.log('1 document inserted');
        db.close();
      });
    }
  }
  for (var key in mongoData.Categorys) {
    if (!existsInDatabase(mongoData.Customers[key], 'Customers')) {
      db.db(dbName).collection('Categorys').insertOne(mongoData.Categorys[key], function(err, res) {
        if (err) throw err;
        console.log('1 document inserted');
        db.close();
      });
    }
  }
});

function existsInDatabase(obj, collection) {
  var result = false;
  MongoClient.connect(mongoData.ConString, {
    useNewUrlParser: true
  }, function(err, db) {
    db.db(dbName).collection(collection).find({}).forEach(function(doc) {
      if (doc.id == obj.id) {
        result = true;
      }
    }, function(err) {
      console.log(err);
    });
  });
  return result;
}

Answer 1

我对你的代码做了一些修改。看来你是异步编程的新手，花点时间了解流程。请随时进行任何进一步的查询。这是您的代码。

// Welcome to aync programming
// Here no one waits for the slow processes


 var MongoClient = require('mongodb').MongoClient;
 var mongoData = require('./mongoData');
 var exports = module.exports = {};
 var dbName = 'checklist';


 // Make the connection for once only 
 MongoClient.connect(mongoData.ConString, { useNewUrlParser: true },       
 function(err, db) {
  if (err) throw err;
 var myDB = db.db(dbName); // create DB for once 

 for (var key in mongoData.Customers) {

     //make call to the function and wait for the response
     existsInDatabase(mongoData.Customers[key], 'Customers', function(err, result) {
         //once the response came excute the next step
         if (result) {
             myDB.collection('Customers').insertOne(mongoData.Customers[key], function(err, res) {
                 if (err) throw err;
                 console.log('1 document inserted');
             });
         }
     });
 }
 for (var key in mongoData.Categorys) {
     //make call to the function and wait for the response
     existsInDatabase(mongoData.Customers[key], 'Customers', function(err, result) {
         //once the response came excute the next step
         if (result) {
             myDB.collection('Categorys').insertOne(mongoData.Categorys[key], function(err, res) {
                 if (err) throw err;
                 console.log('1 document inserted');
             });
         }
     });
 }

 // Both the for loop will work randomly without any order


 function existsInDatabase(obj, collection, cb) {
     var result = false;
     myDB.collection(collection).findOne({ id: obj.id }, function(err, result)     
 {
         if (err) {
             //this cb will work only when db operation is complited
             cb(err);
         } else if (result) {
             cb(null, true);
         } else {
             cb(null, false);
         }
     });
 }
});

此代码可能会导致一些错误。欢迎提出更多问题