我正在尝试映射一个可观察对象,从我返回的可观察对象中获取一个值,然后将该值提供给另一个可观察对象,然后返回该结果。这是我到目前为止的内容:
getJobsByUser(user: User): Observable<Job[]> {
return this.getUsersGroupsAsObservable(user.uid, 'contacts').map(groups => {
groups.map(group => {
this.getJobsbyGroup(group.id);
});
});
getJobsbyGroup(groupId: string): Observable<Job[]> {
return this.afs
.collection<Job>('jobs', ref => ref.where(`group.${groupId}`, '==', true))
.valueChanges();
}
getUsersGroupsAsObservable(
userId: string,
type: string = 'users',
): Observable<Group[]> {
return this.afs
.collection<Group>('groups', ref =>
ref.where(`${type}.${userId}`, '==', true),
)
.valueChanges();
}
问题是 typescript 表明我的getJobsByUser函数将返回type:void的可观察对象。当我将其输出到模板上时,我什么也没有得到或未定义。我觉得我需要使用switchMap,但对rx/js有点模糊。我不确定如何返回Job []类型的Observable
更新:在@Pranay Rana的帮助下,我现在正在返回数组,并且可以得到如下第一个值:
getJobsByUser(user: User): Observable<Job[]> {
return this.getUsersGroupsAsObservable(user.uid, 'contacts').pipe(
mergeMap(groups => {
// returns an array of groups - we need to map this
return this.getJobsbyGroup(groups[0].id); // works with the first value - do we need another map here?
}),
);
}
更新2:我设法从firestore中获取了一些数据,但是它发出了多个可观察对象,而不是组合流:
this.fb.getUsersGroupsAsObservable(user.uid, 'contacts')
.switchMap(groups => {
return groups.map(group => this.fb.getJobsbyGroup(group.id));
})
.subscribe(res => {
console.log(res);
// this emits multiple observables rather than one
this.job$ = res;
});
最佳答案
下面的方法在Way to handle Parallel Multiple Requests中进行了详细讨论
下面的方法利用mergemap
getJobsByUser(user: User) {
return this.getUsersGroupsAsObservable(user.uid, 'contacts').pipe(
mergeMap(group => this.getJobsbyGroup( group.id))
);
}
callingfunction(){
const requests = this.getJobsByUser(this.user);
requests.subscribe(
data => console.log(data), //process item or push it to array
err => console.log(err));
}
您也可以使用
forkJoin
getJobsByUser(user: User) {
return this.getUsersGroupsAsObservable(user.uid, 'contacts').pipe(
map(group => this.getJobsbyGroup( group.id))
);
}
callingfunction(){
const requests = forkJoin(this.getJobsByUser(this.user));
requests.subscribe(
data => console.log(data), //process item or push it to array
err => console.log(err));
}
关于angular - 通过映射另一个Observable返回一个Observable,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/50809542/