javascript - 使用 q.js Promise 时出现问题

Question

以下代码使用 q.js 获取学生的详细信息。除了获取的类别和城市未映射到变量 studentdetails 中之外，一切正常。它仅包含邮件查询获取的详细信息(姓名、电子邮件、ID、出生日期)。我哪里错了？任何线索都将受到高度赞赏。

//fetches category of student
var getJobCategories = function(student) {
            var deferred = Q.defer();
            var categoryquery = 'select c.name,c.id from category c,student_category sc where xxxx';
            db.query(categoryquery, function(err, categories, fields) {
                if(categories.length == 0) {
                    student.categories = "NA";
                } else {
                    student.categories = categories;
                }
                console.log(student)//prints details with categories
                deferred.resolve();
            });
            return deferred.promise;

        }
//fetches city of student
        var getCurrentCity = function(student) {
            var deferred = Q.defer();
            var cityquery = 'select l.name,l.id from location l ,student_location sl where xxxx';
            db.query(cityquery, function(err, city) {
                if(city.length == 0) {
                    student.currentcity = "NA";
                } else {
                    student.currentcity = city;    
                }
                console.log(student)//prints details with city
                deferred.resolve();
            });
            return deferred.promise;

        }

        var query='select name,email,id,dob from student limit 1,10'; 
        db.query(query, function(err1, studentdetails) {
             var promise1=studentdetails.map(function(student){ 
           var result=getJobCategories(student)

                 });
                 var promise2=studentdetails.map(function(student){ 
                      getCurrentCity(student)
                 });

             var allpromises= Q.all([
                 promise1,promise2

             ]);

             Q.allSettled(allpromises)
                 .then(function (results) {
                           next(null,{
                         result: studentdetails,
                         msg: "Fetched successfully"
                     });     
                 });//then
        });//query

Answer 1

你可以尝试这个:

db.query(query, function(err1, studentdetails) {
             var allStudentJobCategories = 
                studentdetails.map(function(student){ 
                    return getJobCategories(student)
                });

             var allStudentCities = 
                 studentdetails.map(function(student){ 
                   return getCurrentCity(student)
                 });

             var allpromises= Q.all([
                 Q.all(allStudentJobCategories), Q.all(allStudentCities)
             ]);

             Q.allSettled(allpromises)
              .then(function (results) {
                       next(null,{
                     result: studentdetails,
                     msg: "Fetched successfully"
                 });     
             });//then
    });