I have a very complicated example of chained RxJS calls with a lot of switchMap and etc. Everything is clear for me until I faced one requirement: I need to poll last request every 5 sec until response object contains a value. I stuck a bit... I know how to make it if I have only polling or if I have only plain switchMap.
this.articleService.create(data).pipe(
switchMap((article: ArticleCreateModel) => this.articleService.getArticle(article.id)),
switchMap((article: ArticleCreateModel) =>
this.articleService.update({
...article,
timestamp: this.someFakeService.getData(),
}),
),
// somehow I need to poll next createAsyncCommentsSection every 5 sec until response object key is let's say 'true'
switchMap((article: ArticleCreateModel) => this.articleService.createAsyncCommentsSection(article.id)),
);
How can I poll last switchMap every 5 sec until response object key is let's say 'true'. And retry it only 5 times?
I tried so, but it looks like it doesn't work:
switchMap((article: ArticleCreateModel) =>
this.articleService.createAsyncCommentsSection(article.id).pipe(
delay(5000),
filter((article: ArticleCreateModel) => !!article.hasSyncedWithOtherAPI),
take(5),
),
),
You can create a single observable that polls and emits when response.isComplete like this:
timer(0, 5000).pipe(
take(5),
switchMap(() => this.articleService.createAsyncCommentsSection(articleId)),
filter(response => response.isComplete),
first()
);
timer() will emit immediately, then every 5 seconds; a maximum of 5 times thanks to take(5).
filter prevents emissions until your condition is met.
first will take only 1 emission, but will throw an error if no emission is received before the stream is completed.
So altogether, could look like this:
this.articleService.create(data).pipe(
switchMap((article: ArticleCreateModel) => this.articleService.getArticle(article.id)),
switchMap((article: ArticleCreateModel) =>
this.articleService.update({
...article,
timestamp: this.someFakeService.getData(),
}),
),
switchMap((article: ArticleCreateModel) => timer(0, 5000).pipe(
take(5),
switchMap(() => this.articleService.createAsyncCommentsSection(article.id)),
filter(response => response.isComplete),
first()
)
);