javascript - rxjs 相当于使用 'return' 停止异步函数；

Question

我想实现类似下面的东西(如果使用 promises 就很容易)

async doSomething(sID){
 let student = await service.getStudent(sID);
 let teacher = await service.getTeacher(student.TeacherID);
 if(!teacher.Active){
   return;
 }

 await service.teacherSomething(teacher);
 await service.studentSomething(student);
}

如果我使用 observables 而不是 promises，我不知道如何做到这一点，但这是我到目前为止尝试过的方法

doSomething(sID){
  let student;
  let teacher;
  service.getStudent(sID).pipe(
      switchMap(studentR=>{
        student = studentR;
        return service.getTeacher(student.TeacherID);
      }),
      switchMap(teacherR=>{
        teacher = teacherR;
        if(!teacher.Active){
            return of(null);
        }else{
            return service.teacherSomething(teacher);
        }
      }),
      swicthMap(teacherSomethingResponse=>{
          if(teacherSomethingResponse==null){
              return of(null);
          }else{
            return service.studentSomething(student);
          }
      })
  }).subscribe();

}

如您所见，与 promise 版本相比，我的 rxjs 版本似乎太长了，而且我觉得我的做法不正确。

Answer 1

这是将当前代码转换为 Rx 样式的方法。如果条件不满足，takeWhile 将完成您的可观察

function doSomething(sID) {
  return from(service.getStudent(sID)).pipe(
    switchMap(student =>
      service.getTeacher(student.TeacherID).pipe(
        takeWhile(teacher => teacher.Active),
        switchMap(teacher => service.teacherSomething(teacher).pipe(takeWhile(res => res))),
        switchMap(() => service.studentSomething(student))
      )
    ))
}