Using RxJs ConcatMap don't send a value of null or empty string

Question

I am using RxJs concatMap to control the saving of some data in my application.

this.myService.saveData(this.updatedData)
  .pipe(
    tap(data1Res => this.onData1Success(data1Res)),
    concatMap(() => this.myService.saveOne(this.OneData)),
    tap(data2Res => this.onData2Success(data2Res)),
    concatMap(() => this.myService.saveTwo(this.TwoData)),
    tap(data3Res => this.onData3Success(data3Res)),
    concatMap(() => this.myService.saveThree(this.ThreeData)),
    tap(data4Res => this.onData4Success(data4Res)),
    concatMap(() => this.myService.saveFour(this.FourData)),
  )
  .subscribe(
    res => this.onSaveSuccess(), // Reload values
    err => console.log('error while saving', err) // Save to file or db
  );

Currently this works however it also executes even if say "this.OneData" is empty or null...how can I keep it from sending essentially a NoOpp request?

you can use filter(r => r !== null ) to filter nulls or anything else — Barkha
– Barkha, Commented Feb 26, 2020 at 16:50
Thanks for the response so what would the call look like exactly...concatMap(filter(() => this.myService.saveOne(this.OneData) !== null)) — Funn_Bobby
– Funn_Bobby, Commented Feb 26, 2020 at 16:54

Cenk Çetinkaya · Accepted Answer · 2020-02-26 17:14:18Z

1

this.myService.saveData(this.updatedData)
  .pipe(
    tap(data1Res => this.onData1Success(data1Res)),
    concatMap(() => this.myService.saveOne(this.OneData)),
    filter(res => res !== null),
    tap(data2Res => this.onData2Success(data2Res)),
    ...

  )
  .subscribe(
    res => this.onSaveSuccess(), // Reload values
    err => console.log('error while saving', err) // Save to file or db
  );

answered Feb 26, 2020 at 17:14

Cenk Çetinkaya

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5 Comments

Funn_Bobby Over a year ago

Thank you for the response Cenk ...so this will not call "saveOne" if "this.OneData" is Null?

Cenk Çetinkaya Over a year ago

If the saveOne's res is null then the others are not called. Filter breaks the pipe when the value is false.

Funn_Bobby Over a year ago

Okay, what if I want "saveTwo" and " saveFour" to execute because "this.TwoData" and "this.FourData" are populated but I don't want the others to execute because they are not populated...doesn't sound like "filter" will work for that.

Cenk Çetinkaya Over a year ago

Actually this pipe usage is not efficient, I don't understand what you completely do.

Funn_Bobby Over a year ago

It's usage is to call api's in a certain order one after another to avoid nested .subscribes...so for that it's pretty efficient.

Barkha · Accepted Answer · 2020-02-27 11:29:02Z

0

Filter can be used like this to make sure it doesn't run if it is empty or null

this.myService.saveData(this.updatedData)
  .pipe(
    tap(data1Res => this.onData1Success(data1Res)),
    filter(res => res),
    concatMap(() => this.myService.saveOne(this.OneData)),
   ...
  )
  .subscribe(
    res => this.onSaveSuccess(), // Reload values
    err => console.log('error while saving', err) // Save to file or db
  );

answered Feb 27, 2020 at 11:29

Barkha

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