Question

我试图了解async / await和Promise函数。然而经过大量的努力和研究，我找不到任何简单的方法来使用我的4 for循环。

如果Javascript不是异步的话，我会告诉你代码应该如何。你能告诉我在哪里（以及如何）我可以通过承诺让我的代码按预期工作吗？

function (courses) {
    var lines = [];
    for (var i = 0; i < courses.length; i++) {
        var course = courses[i];
        var sessions = course.sessions;
        var students = course.students;
        var skills = course.skills;
        console.log('\nCourse : ' + course);

        for (var j = 0; j < sessions.length; j++) {
            var session = sessions[j];
            console.log('\nSession : ' + session);

                for (var k = 0; k < students.length; k++) {
                    var student = students[k];
                    console.log('\nStudent : ' + student);

                    for (var l = 0; l < skills.length; l++) {
                        var skill = skills[l];
                        console.log('\nSkill : ' + skill);
                        Evaluation.findOne({
                            student_id: student._id,
                            session_id: session._id,
                            skill_id: skill._id
                        }).exec(function (err, eval) {
                            console.log('\nStudentID : ' + eval);
                            console.log('\nSessionID : ' + eval);
                            console.log('\nSkillID : ' + eval);
                            console.log('\nEval : ' + eval);
                            var line = [];
                            line.push(course.name);
                            line.push(session.date);
                            line.push(student.firstname);
                            line.push(student.name);
                            if (eval) {
                                line.push(eval.name);
                                line.push(eval.mark);
                            }
                            else {
                                line.push(skill.name);
                                line.push('Not Evaluated');
                            }
                            lines.push(line)
                        })
                    }
                }
            }
        }
    return lines;
}

Answer 1

假设您使用mongoose，您需要更改的只是替换

client.time_series("https://api.fitbit.com/1/user/-/activities/heart/date/today/1d.json", period="1d")

通过

Evaluation.findOne({
    student_id: student._id,
    session_id: session._id,
    skill_id: skill._id
}).exec(function (err, eval) {
    console.log('\nStudentID : ' + eval);
    console.log('\nSessionID : ' + eval);
    console.log('\nSkillID : ' + eval);
    console.log('\nEval : ' + eval);
    var line = [];
    line.push(course.name);
    line.push(session.date);
    line.push(student.firstname);
    line.push(student.name);
    if (eval) {
        line.push(eval.name);
        line.push(eval.mark);
    } else {
        line.push(skill.name);
        line.push('Not Evaluated');
    }
    lines.push(line)
})

因为所有方法都已经返回类似承诺的对象，您可以直接const eval = await Evaluation.findOne({ // ^^^^^ student_id: student._id, session_id: session._id, skill_id: skill._id }); console.log('\nStudentID : ' + eval); console.log('\nSessionID : ' + eval); console.log('\nSkillID : ' + eval); console.log('\nEval : ' + eval); var line = []; line.push(course.name); line.push(session.date); line.push(student.firstname); line.push(student.name); if (eval) { line.push(eval.name); line.push(eval.mark); } else { line.push(skill.name); line.push('Not Evaluated'); } lines.push(line)，而不是使用await并传递节点回传。

Answer 2

看起来你在这里尝试做两件事：你想要异步循环课程/课程/学生/技能，并进行相当耗时的Evaluation.findOne电话。

我建议使用async.forEach替换部分或全部for循环。您还可以将Evaluation.findOne块放入包含在Promise中的辅助函数中，但考虑到它在执行后被lines推送到function (courses) { var lines = []; for (var i = 0; i < courses.length; i++) { var course = courses[i]; var sessions = course.sessions; var students = course.students; var skills = course.skills; console.log('\nCourse : ' + course); for (var j = 0; j < sessions.length; j++) { var session = sessions[j]; console.log('\nSession : ' + session); for (var k = 0; k < students.length; k++) { var student = students[k]; console.log('\nStudent : ' + student); skills.forEach(function(skill) { console.log('\nSkill : ' + skill); buildStudentLine(student, session, skill, course) .then((line )=> { lines.push(line); }) .catch((error) => { console.log(error); }) }); } } } return lines; } function buildStudentLine(student, session, skill, course) { return new Promise((resolve, reject) => { Evaluation .findOne({ student_id: student._id, session_id: session._id, skill_id: skill._id }) .exec(function (err, evaluated) { var line = []; line.push(course.name); line.push(session.date); line.push(student.firstname); line.push(student.name); if (evaluated) { line.push(evaluated.name); line.push(evaluated.mark); } else { line.push(skill.name); line.push('Not Evaluated'); // possibly put this in here if you don't want the line to enter the lines array: // reject('Not Evaluated'); } resolve(line); }); }); }。是一个可选的举动。

执行以下操作：技能迭代现在使用async.forEach，而行构建器就在承诺中。

foo AND bar

无法确定Async / Await和Promises是否正常工作

2 个答案: