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[英]RxJs | How to delay `mergeMap` to moment when previous inner observable completes?
[英]Rxjs angular 6/7 mergeMap delay http request
我想使用此代碼發送請求(我也嘗試過forkJoin),並且在調用之間有延遲:
duplicateElement(id: string): Observable<any> {
return this.http.get({ routeName: 'route_name', params: { id } });
}
duplicateElements(ids: string[]): Observable<any> {
return from(ids)
.pipe(
mergeMap(id => this.duplicateElement(id).pipe(delay(1000))
));
}
但.pipe(延遲(1000)無法正常工作:1000毫升后發送每個http請求。
import * as rx from "rxjs";
import * as rxop from "rxjs/operators";
const startTime = new Date();
function getTimestamp() {
return (new Date().getTime() - startTime.getTime()) / 1000;
}
const desiredDelay = 750;
const serviceDelay = 500;
// simulating service, you can ignore what's inside
var myService = (b: any) => {
return rx.of(Math.random()).pipe(
// To simulate long running service
rxop.delay(serviceDelay),
// Log the timestap after execution, should be ~ desiredDelay + serviceDelay, so by default 1250ms each emitted value
rxop.tap(() => console.log(`${b} after service result, ${getTimestamp()}`)),
// simulating the result
rxop.map(a => "result" + b)
);
};
of([1, 2, 3, 4, 5])
.pipe(
// See the initial values
tap(console.log),
// Split array into single values during emit
// Collect observables and subscribe to next when previous completes
concatAll(),
// Emit each value as a sequence of observables with a desired delay
concatMap(a => of(a).pipe(delay(desiredDelay))),
// Call service on each value as soon as possible, do not care about the order
mergeMap(a => myService(a)),
// Reduce single values back into array
// Reduces the values from source observable to a single value that's emitted when the source completes
reduce<any>((acc, val) => [...acc, val], []),
// See the result, not necessary
tap(console.log)
)
.subscribe();
of([1, 2, 3, 4, 5])
.pipe(
// See the initial values
tap(console.log),
// Split array into single values during emit
// Collect observables and subscribe to next when previous completes
concatAll(),
// Call the service
// Map values to inner observable, subscribe and emit in order
concatMap(a => myService(a).pipe(delay(desiredDelay))),
// Reduce single values back into array
// Reduces the values from source observable to a single value that's emitted when the source completes
reduce<any>((acc, val) => [...acc, val], []),
// See the result, not necessary
tap(console.log)
)
.subscribe();
這個怎么樣:
duplicateElements(ids: string[]): Observable<any> {
return interval(1000).pipe( // start emitting every 1000ms
take(ids.length), // limit emissions to length of array
map(i => ids[i]), // map (change) emission to the array item @ index i
mergeMap(id => this.duplicateElement(id)) // add the http request
)
}
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