Got some problems with observable. I have a function, with one returns me an Observable.

public getData(userId) {
    const data = this.execute({userId: userId});
    return {event: "data.get", data: data}
}

private execute(input: SomeDto):  Observable<SomeRefType[]> {
    return this.databaseGateway.queryMany(DatabaseCommand.WebRecordGetbyparticipantid, {
      parameters: {
        prm_contextuserid: input.userId,
        prm_filterparticipantids: null,
        prm_filtertext: null
      }
    }).pipe(map(res => res));
  }

Type what pipe(map) returns

What I'm got when trying to return or log data

Question: Why .pipe(map(res => res)) don't work? What am I doing wrong?

For sure, I can read data from .pipe(take(1)).subscribe(data => console.log(data)), but, how can I return data from construction like this?

Thanks everyone! Have a good day!

CodePudding user response：

As said in the Rxjs documentation observable are lazy computation.

It means the as long as you don't subscribe to them they won't do anything. It exists two ways to trigger a subscription.

Either within a ts file using .susbcribe() or within a view when calling an endpoint.

If you're using nestjs it would be when calling the url defined within a @Controller('') with an http verb like @Get('path')

By convention you suffix observable variables with $: data$ = new Observable<any>().

CodePudding user response：

At some point you'll have to convert the observable to a promise. Best to do it early and convert it using firstValueFrom immediately after the query. Then convert your caller to an async method to use the returned value.

public async getData(userId): Promise<{ event: string, data: SomeRefType[] }> {
  const data = await this.execute({userId: userId});
  return { event: 'data.get', data };
}

private execute(input: SomeDto):  Promise<SomeRefType[]> {
  const res$ = this.databaseGateway.queryMany(DatabaseCommand.WebRecordGetbyparticipantid, {
    parameters: {
      prm_contextuserid: input.userId,
      prm_filterparticipantids: null,
      prm_filtertext: null
    }
  });
  return firstValueFrom(res$);
}