使用事件

Question

所以目前正在开发一个可以完成相当多数据库工作的应用程序，并认为解决这个问题的一种聪明方法应该是使用事件。因此，我为应用程序设置了一个事件发射器，然后使用它作为控制流的方法。我有点假设事件发射器的工作方式与消息队列类似。

情况并非如此，由于某种原因，我不能让偶数发射器在第二次调用同一函数时按预期工作。

我会理解，如果问题是它多次调用，但实际上，下面的代码将运行第二个函数两次，但只会传递dbEvents.once('Ready'一次。我不仅无法弄清楚为什么，它似乎不断地工作，并且永远不会打印出来＆＃34;写第四个＆＃34;

var mongo = require('mongodb');
var events = require('events');
var dbEvents = new events.EventEmitter();




function writeStuff(first, second, status, cuID){
        console.log('Wrote '+ first);
        if (status === 1) {
            console.log('\t\tReady for '+ cuID);
            dbEvents.emit('Ready');
        } else {
            console.log('\t\tReady (but not 1) for ' + cuID);
            dbEvents.emit('Ready');
        }
        console.log('\t\tjust about to kick of number ' + status);
        dbEvents.once('Ready', function (condata) {
            console.log('Wrote '+ second)
            dbEvents.emit('Done'+cuID)

        });

}

var cuID1 = mongo.ObjectID();
writeStuff('First', 'Second', 1, cuID1);
dbEvents.on('Done'+cuID1, function(){
    console.log('\tFirst completed ' + cuID1);
});

var cuID2 = mongo.ObjectID();
writeStuff('Third', 'Forth', 2, cuID2);

dbEvents.on('Done'+cuID2, function(){
    console.log("\tSecond completed " + cuID2)
});

var b = 0;
for(var i = 0; i < 100000000; i++){
    b++;
}
console.log("And I counted to " + b);

运行上述代码时的输出如下所示

Wrote First
                Ready for 5540c57cd8fa9555076f9aba
                just about to kick of number 1
Wrote Third
                Ready (but not 1) for 5540c57cd8fa9555076f9abb
Wrote Second
        First completed 5540c57cd8fa9555076f9aba
                just about to kick of number 2
And I counted to 100000000

================更新==============

为什么我无法生成活动，I.E。如果我使用唯一标识符，我似乎不能将其作为事件发送。在这种情况下，我将事件更改为Ready + cuID（mongodb），现在第二次写入永远不会被调用。

var mongo = require('mongodb');
var events = require('events');
var dbEvents = new events.EventEmitter();




function writeStuff(first, second, status, cuID){
        console.log('Wrote '+ first);
        if (status === 1) {
            console.log('\t\tReady for '+ cuID);
            var flag = 'Ready'+cuID
            dbEvents.emit(flag);
        } else {
            console.log('\t\tReady (but not 1) for ' + cuID);
            dbEvents.emit('Ready');
        }
        console.log('\t\tjust about to kick of number ' + status);
        dbEvents.once(flag, function (condata) {
            console.log('Wrote '+ second)
            dbEvents.emit('Done'+cuID)

        });

}

var cuID1 = mongo.ObjectID();
writeStuff('First', 'Second', 1, cuID1);
dbEvents.on('Done'+cuID1, function(){
    console.log('\tFirst completed ' + cuID1);
});

var cuID2 = mongo.ObjectID();
writeStuff('Third', 'Forth', 2, cuID2);

dbEvents.on('Done'+cuID2, function(){
    console.log("\tSecond completed " + cuID2)
});

var b = 0;
for(var i = 0; i < 1000000000; i++){
    b++;
}
console.log("And I counted to " + b);