[英]Combining observables in series & parallel to fetch data from multiple APIs
I am trying to check the validity of a function I have written in Typescript, in congruence with RxJS observables, that fetches some bookings from one service and then for each booking fetches its corresponding location and activity from another service. I am trying to check the validity of a function I have written in Typescript, in congruence with RxJS observables, that fetches some bookings from one service and then for each booking fetches its corresponding location and activity from another service.
I am simply writing this post to verify the validity of what I have written and to ask if there is anything I could have done more efficiently.我写这篇文章只是为了验证我所写内容的有效性,并询问是否有什么我可以做的更有效。
let params = new HttpParams();
params = params.append('status', 'C');
params = params.append('offset', offset.toString());
params = params.append('limit', limit.toString());
return this.http.get(`${this.environment.booking.url}/my/bookings`, { params }).pipe(
mergeMap((bookings: Booking[]) => {
if(bookings.length > 0) {
return forkJoin(
bookings.map((booking: Booking) =>
forkJoin(
of(booking),
this.activityService.getActivity(booking.activity),
this.locationService.getLocation(booking.finalLocation),
).pipe(
map((data: [ Booking, Activity, Location ]) => {
let booking = data[0];
booking.activityData = data[1];
booking.finalLocationData = data[2];
return booking;
})
)
)
)
}
return of([]);
}),
catchError((err: HttpErrorResponse) => throwError(err))
);
I am expecting for this function to return a list of bookings alongside their corresponding location and activity.我期待这个 function 返回一个预订列表以及相应的位置和活动。 However more importantly I want to verify that what I am doing is correct and sensible.但更重要的是,我想验证我所做的是否正确和明智。 Is there anything I could have done differently to make it cleaner/ more human-readable (not nit-picking, please )?有什么我可以做的不同的事情来使它更清晰/更易于阅读(请不要吹毛求疵)?
On a different note, that of performance, I also have a follow-up question with regards to performance.另一方面,关于性能,我还有一个关于性能的后续问题。 Given that a list of bookings has common activities and locations.鉴于预订列表具有共同的活动和位置。 Is there a way to only fetch activities and locations without any duplicate HTTP requests?有没有办法只获取活动和位置而没有任何重复的 HTTP 请求? Is this already handled under the hood by RxJS?这是否已经由 RxJS 在后台处理? Is there anything I could have done to make this function more efficient?我能做些什么来让这个 function 更高效吗?
This is how I would tackle this using RxJS:这就是我使用 RxJS 解决这个问题的方法:
Bookings
获取所有Bookings
Location
and Activities
cuncurrently对于每个预订,同时获取Location
和Activities
const { from, of, forkJoin, identity } = rxjs; const { mergeMap, tap, catchError } = rxjs.operators; const api = 'https://jsonplaceholder.typicode.com'; const endpoints = { bookings: () => `${api}/posts`, locations: (id) => `${api}/posts/${id}/comments`, activities: (id) => `${api}/users/${id}` }; const fetch$ = link => from(fetch(link)).pipe( mergeMap(res => res.json()), catchError(() => from([])), ); fetch$(endpoints.bookings()).pipe( mergeMap(identity), mergeMap(booking => forkJoin({ booking: of(booking), locations: fetch$(endpoints.locations(booking.id)), activities: fetch$(endpoints.activities(booking.userId)), })), ).subscribe(console.log);
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/6.5.3/rxjs.umd.js" integrity="sha256-Nihli32xEO2dsnrW29M+krVxoeDblkRBTkk5ZLQJ6O8=" crossorigin="anonymous"></script>
note :注意:
filter
operator.要丢弃空预订,您可以使用filter
运算符。forkJoin
also takes a spec object which is very useful (part of the overloads)forkJoin
还采用了一个非常有用的规范 object (部分重载)I'm not sure about the efficiency, but, at least for me, it was a little hard to read我不确定效率,但是,至少对我来说,它有点难以阅读
Here's how I'd do it:这是我的做法:
I used a dummy API, but I think it correlates with your situation我使用了一个虚拟 API,但我认为它与您的情况有关
const usersUrl = 'https://jsonplaceholder.typicode.com/users';
const todosUrl = 'https://jsonplaceholder.typicode.com/todos';
const userIds$ = of([1, 2, 3]); // Bookings' equivalent
userIds$
.pipe(
filter(ids => ids.length !== 0),
// Flatten the array so we can avoid another nesting level
mergeMap(ids => from(ids)),
// `concatMap` - the order matters!
concatMap(
id => forkJoin(ajax(`${usersUrl}/${id}`), ajax(`${todosUrl}/${id}`))
.pipe(
map(([user, todo]) => ({ id, user: user.response, todo: todo.response }))
)
),
toArray()
)
.subscribe(console.log)
Here is a StackBlitz demo.这是一个 StackBlitz 演示。
With this in mind, here is how I'd adapt it to your problem:考虑到这一点,这是我如何适应您的问题的方法:
this.http.get(`${this.environment.booking.url}/my/bookings`, { params }).pipe(
filter(bookings => bookings.length !== 0),
// Get each booking individually
mergeMap(bookings => from(bookings)),
concatMap(
b => forkJoin(
this.activityService.getActivity(b.activity),
this.locationService.getLocation(b.finalLocation),
)
.pipe(
map(([activity, location]) => ({ ...b, activity, location }))
)
),
// Getting the bookings array again
toArray()
catchError((err: HttpErrorResponse) => throwError(err))
);
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.