Mongodb.connect不执行回调函数

Question

我试图连接到我的Mongodb并插入一些文档，如果它们还没有在数据库中。它与第一次插入一起工作，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更改。看来你是异步编程的新手，花一些时间了解流程。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。随意提出更多问题

Answer 2

db.db(dbName).collection(collection).find({})根据文档返回游标。您缺少.toArray()：

db.db(dbName).collection(collection).find({}).toArray()...