循环中的MongoDB被跳过（Node.js）

Sorry for asking noob question (Below code is associated with express framework and mongoose DB)

很抱歉询问noob问题(下面的代码与快速框架和mongoose DB相关)

I'm trying to loop through the array 'Users' that contains usernames, then I try to match them on mongoose database to get the school and the grade for each user. Then combine them into on final array called UsersInfoFinal .

我正在尝试遍历包含用户名的数组'Users',然后我尝试在mongoose数据库上匹配它们以获得学校和每个用户的等级。然后将它们组合到名为UsersInfoFinal的最终数组中。

var Users = ['peter', 'john'];
var UsersInfoFinal = [];

for (i = 0; i < Users.length; i++){
    userModel.findOne ({username: Users[i]}, 'username school grade', function (error, UserInfo) {
        UsersInfoFinal .push([UserInfo.username, UserInfo.school, UserInfo.grade]);
    });
}
console.log(UsersInfoFinal );

The console should print [[peter, MIT, 95], [john, Royal Academy, 89]], however, the console still prints [], the variable UsersInfoFinal isn't modified.

控制台应该打印[[peter,MIT,95],[john,Royal Academy,89]],但是,控制台仍然打印[],不修改变量UsersInfoFinal。

Why is that? Is there a way to modify the variable after the loop? Help please I'm really new to node.js and MongoDB and have been stuck for hours :S

这是为什么?有没有办法在循环后修改变量?请帮助我对node.js和MongoDB真的很新,并且已经被困了几个小时:S

Thanks!

1 个解决方案

#1

Here I will give you a very simple pattern for use in cases like this. Try this code:

在这里,我将为您提供一个非常简单的模式,以便在这种情况下使用。试试这段代码:

var Users = ['peter', 'john'];
var UsersInfoFinal = [];

var usersWaiting = 0;

function allDone() {
  console.log(UsersInfoFinal);
}

for (i = 0; i < Users.length; i++){
    usersWaiting++;
    userModel.findOne ({username: Users[i]}, 'username school grade', function (error, UserInfo) {
        usersWaiting--;
        UsersInfoFinal .push([UserInfo.username, UserInfo.school, UserInfo.grade]);
        if (usersWaiting == 0) {
          allDone();
        }
    });
}

This is a pretty common pattern for managing multiple asynchronous calls in ecmascript environments. There may be a better way to do it but it sure gets the job done.

这是在ecmascript环境中管理多个异步调用的一种非常常见的模式。可能有更好的方法,但它确实可以完成工作。

#1