CODEWITHSUNDEEP
rxjsnestjs
xxx_coder_noscope
xxx_coder_noscope

Reputation: 85

RxJS handling promise rejection

I have a DB query call e.g. getUserByIdOrThrow(id: number): User; How can I properly handle possible promise rejection after getUserByIdOrThrow call? In case of an error, I need to ignore it completely, but if promise resolved successfully, I need to call another async function.

Example flow:

         DBCallAsync
       /            \
    resolved       rejected
     /                \
 another call       do nothing

That how I tried to approach this problem (not working as I expected):

from(this.dbService.getUserByIdOrThrow(100)).pipe(
  tap(({ phone }) => {
    from(this.userService.sendMessage(phone, "hello")).pipe(
      catchError((err) => {
        // doesnt catches
        return EMPTY;
      }),
    )
  }),
catchError((err) => {
  // doesnt catches
  return EMPTY;
}));

How can I implement this in the right way?

Upvotes: 0

Views: 1743

Answers (1)

Rafi Henig
Rafi Henig

Reputation: 6424

Since both functions return Promise I wouldn't recommend of using an Observable, you would be much better handling it in a Promise way:

try {
  const { phone } = await this.dbService.getUserByIdOrThrow(100);
  await this.userService.sendMessage(phone, "hello"))
} catch (error) {

}

Or using RXJS style if you are insist on using it (switchMap operator is used for returning and flattaning an inner obsevable, in addition there's no need to use from inside switchMap since it can handle Promises)

from(this.dbService.getUserByIdOrThrow(100))
  .pipe(
    switchMap(({ phone }) => this.userService.sendMessage(phone, "hello")),
    catchError((err) => EMPTY)
   );

Upvotes: 2

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