javascript - 我的回调没有像预期的那样运行 node js

Question

我想做的是首先从学生集合中获取特定年级和类(class)的所有学生。然后使用请求的年级和类(class)中的学生 ID，使用 mongoose 从 Marks 集合中使用这些学生 ID 找到标记

这是我的学生模式

const StudentSchema = new Schema({
    base_no:{
        type: String,
        required: true 
    },
grade: {
        type: Number,
        required: false
    },
    class: {
        type: String,
        required: false
    }

});

const Student = module.exports = mongoose.model('student',StudentSchema,'student');

然后我在学生模型中有一个这样的方法来获取特定年级和特定类(class)的所有学生

/**
 *  Get all students of a class for a given grade
 * 
 */
module.exports.getStudentsGradeClass = function(params,callback){
    Student.find({grade: params.grade, class: params.class},'base_no first_name last_name').sort({base_no: 1}).exec(callback);
}

这是我的标记模式

 const MarksSchema = new Schema({

        verifire: {
            type: String,
            required: true,
            //index:true
        },
        student_base_id: { // as student auto gen key/index no
            type: String,
            required: true,
            //index:true
        },
        subject_id: {
            type: String,
            required: true,
            ref: 'subject',
            //index:true
        },
        total: {
            type: Number,
            required: true
        }
    });


    const Marks = module.exports = mongoose.model('school_marks', MarksSchema, 'school_marks');

所以我正在使用上面的 Student Schema 的 getStudentsGradeClass()从客户端获取请求学生的方法然后使用此代码使用来自 getStudentsGradeClass() 方法的学生 ID 从 Marks 模式获取分数

    /**
         *  Get marks of all students of the requested grade->class with subject_id
         * 
         */
        module.exports.getClassResults = function (params, callback) {
            let marks = [];
            Student.getStudentsGradeClass({ grade: params.grade, class: params.class }, (err, students) => {
                if (!err) {
                    for (let i = 0; i < students.length; i++) {
                        Marks.find({ subject_id: params.subject_id, student_base_id: students[i].base_no }, 'student_base_id total', (err, data) => {
                            if (!err) {
                                marks.push(data[0]);
                            } else {
                                callback(err, null);
                            }
                        });
                    }
                    callback(null,marks); // this is the function I wan to invoke
                                          // right after the for loop finishes so 
                                          // that i can get all marks of all 
                                          //students for a specific subject..   


    // currently it is undefined(marks[]) coz it goes straight for the callback 
     //  giving control to the for loop, the for loop gives data much later so that 
    // marks are not pushed to the array when I call it.

                } else {
                    callback(err, null);
                }

            });
        }

那么我可以这样做吗(我知道我在厄运金字塔中)。请给我一个更简洁的方法来做到这一点，或者你能指导我克服这个问题或者如何实现我想要达到的目标。非常感谢任何帮助。

Answer 1

你可以试试 async/await......

 module.exports.getClassResults =  (params, callback)=> {
            let marks = [];
            Student.getStudentsGradeClass({ grade: params.grade, class: params.class },async (err, students) => {
                if (!err) {

                 for (let student of students){
                      let data=await Marks.find({ subject_id: params.subject_id, student_base_id: student.base_no }, 'student_base_id total')
                            if (data) {
                                marks.push(data[0]);

                            } else {
                                callback(err, null);
                            }

                    }
                    callback(null,marks); // this is the function I wan to invoke
                                          // right after the for loop finishes so 
                                          // that i can get all marks of all 
                                          //students for a specific subject..   


    // currently it is undefined(marks[]) coz it goes straight for the callback 
     //  giving control to the for loop, the for loop gives data much later so that 
    // marks are not pushed to the array when I call it.

                } else {
                    callback(err, null);
                }

            });
        }