如何在Angular 2中"链接"两个单独的可观察量

Question

我正在使用Angular2开发一个Web应用程序,我从服务器获取数据时遇到了一些问题.

 import ...

 @Component({
 ...

 })
 export class EmployeeManagementTableComponent implements OnInit, OnDestroy{

private employees: Employee[];
private departments: SelectItem[] = [];
private selectedDepartment: string;
private columns: any[];
private paramSub: any;
private employeesSub: any;
private departmentSub: any;


constructor(private employeeManagementService: EmployeeManagementService, 
            private route: ActivatedRoute, 
            private router: Router,
            private ccs: ComponentCommunicatorService,
            private logger: Logger) { }

ngOnInit(){

    this.columns = [
     ...
    ];

    //ccs is just a service for storing/getting app wide infomation

    this.selectedDepartment = this.ccs.getSelectedDepartment();
    this.getDepartments();
    this.getEmployees(this.selectedDepartment);

    ...
}

ngOnDestroy(){
    /*this.employeesSub.unsubscribe();
    this.departmentDub.unsubscribe();*/
}

getDepartments(){

    this.departments.push({label: 'Alle', value: 'all'});

    this.departmentSub = this.employeeManagementService.getDepartments().subscribe(
          data =>  {data.forEach((item, index) => {
                        this.departments.push({label: item, value: index.toString()});
                    });    
                   },
          err => this.logger.error(err),
          () => {this.logger.log('done loading');
                 this.departmentSub.unsubscribe()}
    );
}
getEmployees(department: any){

this.employeesSub = this.employeeManagementService.getEmployees(department).subscribe(
          data => {this.employees = data},
          err => this.logger.error(err),
          () => {this.logger.log('done loading');
                 this.employeesSub.unsubscribe()}
    );
}

正如您所看到的那样,当组件被初始化时,它会调用两个获取数据的方法.这些方法从我的服务中获得可观察性并订阅它们.
问题是订单就像call1, call2, result1, result2, ...,我认为有些事情是不对的.它应该是call1, result1, call2, result2, ...或者我错了？我尝试在observable1中订阅observable2,onComplete但我认为专用方法将毫无用处.我已经研究并找到了一些解决方案,同时使用concat订阅了两个observable,但我只是希望代码在所有数据流量完成后继续在getDepartments()之后继续.

而且我应该在退订OnDestroy()或OnComplete在的subscribe功能我真的不明白有什么区别？

Answer 1

如果要控制observable的执行顺序,则需要构建一个利用运算符的异步数据流flatMap(如串行执行)或Observable.forkJoin(并行执行)

这是样品:

// Series
someObservable.flatMap(result1 => {
  return someOtherObservable;
}).subscribe(result2 => {
  (...)
  (...)
});

// Parallel
Observable.forkJoin([ someObservable, someOtherObservable ])
  .subscribe(results => {
    let result1 = results[0];
    let result2 = results[1];
  });