Question

我是节点js中的新手，并且遇到了带有db返回的回调控制流的问题。

我想要的是以下顺序：

console.log('>>>>>>>  first log in F1   >>>>>>');
console.log('>>>>>>>  second log in F1   >>>>>>');
console.log('>>>>>>>  first log in F2   >>>>>>');
console.log('>>>>>>>  second log in F2   >>>>>>');
console.log('>>>>>>>  first log in F3   >>>>>>');
console.log('>>>>>>>  second log in F3   >>>>>>');
console.log('>>>>>>>  first log in F4   >>>>>>');
console.log('>>>>>>>  second log in F4   >>>>>>');
console.log('>>>>>>>  third log in F4   >>>>>>');
console.log('finished ');

但我没有按顺序进行。代码如下所示：

F1(req).then(function(result){
    return F2(result);
    }).then(function(result){
        return F3(result);
    }).then(function(result){
        return F4(result);
    }).then(function(result){
        console.log('finished ');
    })

var F1 = function(req) {
    return new Promise(function(resolve, reject) {
        console.log('>>>>>>>  first log in F1   >>>>>>');
        var result = {};
        result.emailId = req.body.emailId;
        common.db.collection('document1').findOne({email: req.body.emailId}, function (error, document1object) {
            console.log('>>>>>>>  second log in F1   >>>>>>');
        }); 
        resolve(result);
    });
};
var F2 = function(result) {
    console.log('>>>>>>>  first log in F2   >>>>>>');
    return new Promise(function(resolve, reject) {
        common.db.collection('document2').findOne({email: result.emailId}, function (err, document2object) {
                console.log('>>>>>>>  second log in F2   >>>>>>');
                result.value1 = document2object._id;
        }); 
        resolve(result);
    });
};
var F3 = function(result) {
    console.log('>>>>>>>  first log in F3   >>>>>>');
    return new Promise(function(resolve, reject) {
        common.db.collection('document3').insertOne({email: result.emailId}, function (errr, document3object) {
            console.log('>>>>>>>  second log in F3   >>>>>>');
            result.value2 = document3object.insertedId;
        });
        resolve( result);
    });
};
var F4 = function(result) {
    console.log('>>>>>>>  first log in F4   >>>>>>');
    return new Promise(function(resolve, reject) {
        client.post("urlPart1"+result.value2+"urlPart2", 
        args, function (data, response) {
           console.log('>>>>>>>  second log in F4   >>>>>>');
        });
        console.log('>>>>>>>  third log in F4   >>>>>>');
        resolve( result);
    });
};

提前谢谢你：）

Answer 1

因为......异步。

您的请求会同时进行所有评估，因此您无法按照所需的顺序获取日志。如果你想要一个特定的订单，你必须在最后一个请求完成后开始下一个请求，即在前一个请求的回调函数中。

在节点js中使用db返回来控制回调流

1 个答案: