MongoDB回调未引发参考错误 [英] Reference error is not thrown from MongoDB callback

问题描述

所有人都知道，如果我们调用undefined.test，将会收到以下错误(NodeJS和Javascript相同)

All people know that if we call undefined.test we will receive the following error (same for both: NodeJS and Javascript):

$ node
> undefined.test
TypeError: Cannot read property 'test' of undefined
    at repl:1:11
    at REPLServer.self.eval (repl.js:110:21)
    at Interface.<anonymous> (repl.js:239:12)
    at Interface.EventEmitter.emit (events.js:95:17)
    at Interface._onLine (readline.js:202:10)
    at Interface._line (readline.js:531:8)
    at Interface._ttyWrite (readline.js:760:14)
    at ReadStream.onkeypress (readline.js:99:10)
    at ReadStream.EventEmitter.emit (events.js:98:17)
    at emitKey (readline.js:1095:12)

是的！

过去一周，我在调试以下问题上浪费了大约30分钟的时间:脚本意外停止并且未引发任何错误.

Passed week I wasted about 30 minutes in debugging the following problem: A script was stopping accidentally and no error was thrown.

我有一个应该作为对象的urls变量:

I had the urls variable that was supposed to be an object:

var urls = settings.urls || {}; 

然后在接下来的几行中，我需要获取作为字符串的urls的shop键:

Then in next lines I needed to get shop key of urls that was a string:

var shop = urls.shop || "/";

我开始添加console.log来查找变量的值:

I started adding console.log to find the values of variables:

console.log(urls);            // undefined
var shop = urls.shop || "/";
console.log("Passed");        // This isn't run.

脚本中的问题是我正在重新定义正在生成urls undefined的新 urls变量，但是问题是:为什么 无法显示读取的未定义属性商店" 没有出现在这里?因为urls确实是undefined.

The problem in my script was that I was redefining a new urls variable that was making the urls undefined, but the question is: why cannot read property "shop" of undefined didn't appear here? Because urls was really undefined.

我们知道，NodeJS和Javascript都在发生以下情况:

We know that the following is happening in both: NodeJS and Javascript:

 var a = 10;
 foo(function () {
     console.log(a); // undefined
     var a = 10;
 });
 function foo(callback) { callback(); } 

问题

在调试问题后，我发现此问题来自Mongo:在Mongo回调中，如果我们调用undefined.something，我们不要会收到错误.

The question

After debugging the problem I found that this problem comes from Mongo: inside of Mongo callbacks if we call undefined.something we DON'T get the error.

我创建了一个小脚本来演示这一点:

I've created a small script that demonstrates this:

var mongo = require("mongodb");

// Mongo server
var server = mongo.Server("127.0.0.1", 27017);
var db = new mongo.Db("test", server, { safe: true });

console.log("> START");

// Open database
console.log("Opening database.");
db.open(function(err, db) {
    if (err) { return console.log("Cannot open database."); }

    // get collection
    console.log("No error. Opening collection.");
    db.collection("col_one", function(err, collection) {
        if(err) { return console.log(err) }

        // do something with the collection
        console.log("No error. Finding all items from collection.");
        collection.find().toArray(function(err, items) {
            if(err) { return console.log(err) }

            console.log("No error. Items: ", items);
            console.log("The following line is: undefined.shop." +
            "It will stop the process.");
            console.log(undefined.test); // THE ERROR DOES NOT APPEAR!
            console.log("> STOP"); // this message doesn't appear.
        });
    });
});

我的问题是:

1. 为什么没有出现错误?是什么原因(将MongoDB源代码一起调试可以找到它.)
2. 为什么调用undefined.something时进程停止?
3. 如何解决?

1. Why the error doesn't appear? Which is the reason? (It would be great to debug together the MongoDB source code to find it.)
2. Why the process is stopped when calling undefined.something?
3. How can be this solved?

我已经创建了一个 Github存储库 ，您可以在其中下载我的小文件演示问题的应用程序.

I've created a Github repository where you can download my small application that demonstrates the issue.

有趣:

如果添加try {} catch (e) {}语句，我们会发现错误，并且过程将继续显示STOP消息.

If we add a try {} catch (e) {} statement we find the error and the process continue showing the STOP message.

try {
    console.log(undefined.test);
} catch (e) {
    console.log(e);
}

日志:

> START
Opening database.
No error. Opening collection.
No error. Finding all items from collection.
No error. Items:  []
The following line is: undefined.shop. It will stop the process.
[TypeError: Cannot read property 'test' of undefined]
> STOP

推荐答案

查看 github.com 在node-mongodb-native驱动程序问题上，您会注意到在1.3.18版本中该问题已解决.但是，我对其进行了测试，但无法正常工作.

Looking on github.com at node-mongodb-native driver issues, you will notice that issue is solved in 1.3.18 version. But, I tested it and it does not work as expected.

这篇关于MongoDB回调未引发参考错误的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！