使用Rxjs过滤可观察

Question

我正在尝试获取当前用户的活动作业列表：

jobListRef$: Observable<Job[]>;
...
this.afAuth.authState.take(1).subscribe(data => {
  if (data && data.uid) {
    this.jobListRef$ = this.database.list<Job>('job-list', query => {
         return query.orderByChild("state").equalTo("active");
    })
    .snapshotChanges().map(jobs => {
         return jobs.map(job => {
              const $key = job.payload.key;
              const data = { $key, ...job.payload.val() };
              return data as Job;
         });
    })
    .filter(val =>
         val.map(job => {
              return (job.employer == data.uid || job.employee == data.uid);
         })
    );
  }
});

问题仅从过滤开始。 根据官方文档，其参数的正确部分应返回布尔值，就像我的情况一样。 但是它仍然返回我整个条目而不过滤它们。

Answer 1

您将返回Array.map调用的结果，请参见其返回值： https : //developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map

看来您可能想使用map而不是filter ：

.snapshotChanges().map(...)
.map(val => val.map(job => {
   return (job.employer == data.uid || job.employee == data.uid);
}));

Answer 2

我相信您想逆转地图和过滤器运算符。

.map((jobs: Job[]) =>
  jobs.filter((job: Job) => job.employer === data.uid || job.employee === data.uid )
);

（ map将一个数组转换为另一个数组， filter以缩小数组）。

或者，您可以将过滤器链接到执行类型转换的地图上，

.map(jobs => {
  return jobs.map(job => {
    const $key = job.payload.key;
    const data = { $key, ...job.payload.val() };
    return data as Job;
  })
  .filter(job => job.employer === data.uid || job.employee === data.uid )
})

Answer 3

不确定是否了解整个问题，但可能类似于：

this.jobListRef$ = this.afAuth.authState
    .filter(data => !!data && !!data.uid)
    .take(1)
    .switchMap(data =>
        this.database.list<Job>('job-list', query => query.orderByChild("state").equalTo("active"))
            .snapshotChanges()
            .map(jobs =>
                jobs.map(job => {
                    const $key = job.payload.key;
                    const data = { $key, ...job.payload.val() };
                    return data as Job;
                })
            )
            .map((jobs: Job[]) =>
                jobs.filter(job => (job.employer == data.uid || job.employee == data.uid))
            )
    );