CODEWITHSUNDEEP
angulartypescriptrxjsswitchmap
Guy E
Guy E

Reputation: 1927

When running 2 observables one after another, getting: Argument of type is not assignable to parameter of type

I have 2 functions that return Observables that I would like to execute one after another. function1 return

Observable<SomeDataObject>

and function2 return type

Observable<Any>

I want that the function that execute them return boolean based of the result of function1. I was managed to do so when running first function1, but now I would like to run function2 first, and I get the error:

"Argument of type '(res: <SomeDataObject>) => boolean' is not assignable to 
 parameter of type '(value:SomeDataObject, index: number) => 
ObservableInput<any>. Type 'boolean' is not assignable to type 
ObservableInput<SomeDataObject>

See my code: This works:

return this.someService.function1().pipe(
  switchMap(f1Result => 
  {
     this.someService.repositpry.f1ResultData = f1Result;
     return this.someService.function2().pipe(
        map(res => 
       {
           if (res) return true;
           else return false;
       }));
   })
 )

This fails:

 return this.someService.function2.pipe( 
  switchMap(f2Result => 
  {
      this.someService.function1().pipe(
       map(f1result => 
       {
           this.someService.repositpry.f1ResultData = f1Result;
       })
    );
    if (f2Result) return true
    else return false;
 }));

Upvotes: -2

Views: 682

Answers (3)

Picci
Picci

Reputation: 17762

In your second example, within the most external pipe, you have

this.someService.function1().pipe(
       map(f1result => 
       {
           this.someService.repositpry.f1ResultData = f1Result;
       })

f1result is an Observable. In the inner pipe you use a map operator. This is different from the first example, the one which is working, since in the first example you use switchMap, which flattens the Observable.

So you may have to use switchMap in the inner pipe as well, followed by a map to return the result you are looking for, something like this

return this.someService.function2.pipe( 
  switchMap(f2Result => 
  {
      this.someService.function1().pipe(
       switchMap(f1result => 
       {
           this.someService.repositpry.f1ResultData = f1Result;
       }.pipe(() => {
           if (f2Result) return true
           else return false;
       }))
    );
 }));

Upvotes: 1

Wilt
Wilt

Reputation: 44356

You do:

this.someService.function2.pipe(
  //...
)

Should it not be:

this.someService.function2().pipe(
  //...
);

Upvotes: 1

Rahul Tokase
Rahul Tokase

Reputation: 1218

You need a concatMap operator to do this.

return this.someService.function1().pipe(
  concatMap(f1Result => 
  {
     this.someService.repositpry.f1ResultData = f1Result;
     return this.someService.function2.pipe(
        map(res => 
       {
           if (res) return true;
           else return false;
       }));
   })
 )

Upvotes: 1

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