Merge map Angular

Question

Can you tell me what am I doing wrong ?

this.scheduleService.GetZones(environment.systemId)
  .pipe(
    mergeMap((zone: Zone) => {
      return this.dashboardService.GetLatestMeasurementValue(environment.systemId, zone.sensorId)
    })
    .subscribe(mois => {
      this.currentMoisture = mois;
    })
  );
}

I get this error: Property 'subscribe' does not exist on type 'OperatorFunction'

score 3 · Accepted Answer · edited Dec 16 '19 at 12:13

3

You cannot subscribe to an operator. You need to subscribe as follows.

this.scheduleService.GetZones(environment.systemId)
    .pipe(
       mergeMap((zone: Zone) => {
          return this.dashboardService.GetLatestMeasurementValue(environment.systemId, zone.sensorId);
       })
     )
    .subscribe(mois => {
      this.currentMoisture = mois;
    })

edited Dec 16 '19 at 12:13

C.OG

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answered Dec 16 '19 at 12:09

Anto Antony

842
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`mergeMap` will keep your `this.scheduleService.GetZones` observable alive. if your services work the way i think they do, i'd consider `switchMap` instead, this will make sure `this.scheduleService.GetZones` will get unsubscribed. – Stavm Dec 16 '19 at 12:15

score 0 · Answer 2 · answered Dec 16 '19 at 12:16

I see we are mapping zone value to the latest measure value by this method name GetLatestMeasurementValue. If you are always interested in the latest value switchMap is a better operator

this.scheduleService.GetZones(environment.systemId)
    .pipe(
       switchMap((zone: Zone) => {
          return this.dashboardService.GetLatestMeasurementValue(environment.systemId, zone.sensorId);
       })
     )
    .subscribe(mois => {
      this.currentMoisture = mois;
    })

And if it is a single time event simple map would also do the job as below :

this.scheduleService.GetZones(environment.systemId)
    .pipe(
       map((zone: Zone) => {
          return this.dashboardService.GetLatestMeasurementValue(environment.systemId, zone.sensorId);
       })
     )
    .subscribe(mois => {
      this.currentMoisture = mois;
    })

Merge map Angular

2 Answers2