What is the best way to link together a varying amount of observables?

Question

What is the best way to link together a varying amount of observables?

Being new to Angular and Observables, I am looking for a way to efficiently chain the call of a service multiple times. Is there a straightforward method using Observables that can achieve this in a more generic manner than traditional methods? (similar to this example).

this.myService.getNodeById(res.parent_id).subscribe(res => {
  this.myService.getNodeById(res.parent_id).subscribe(res => {
     this.myService.getNodeById(res.parent_id).subscribe(res => {
        // logic here as long as res.parents_id is present
     });
  });
});

angular: 12.0.5
typescript: 4.2.3
rxjs: 6.6.0

angular typescript rxjs

Answer 1

Answer №1

To create a recursive method for retrieving nodes by their IDs, consider implementing the following code snippet:

fetchNodeByID(id) {
  return this.customService
    .getNodeById(id)
    .pipe(switchMap((result) => (result.parent_id ? this.fetchNodeByID(result.parent_id) : of(result))));
}

Answer 2

To create a recursive method for retrieving nodes by their IDs, consider implementing the following code snippet:

fetchNodeByID(id) {
  return this.customService
    .getNodeById(id)
    .pipe(switchMap((result) => (result.parent_id ? this.fetchNodeByID(result.parent_id) : of(result))));
}

Answer 3

Answer №2

If you want to create a unique Rx.js operator, consider implementing one that integrates the necessary API calls within switchMap.

type GetNodeFunction<TNode = any, TResponse = any> = (
  response: TNode
) => Observable<TResponse>;

// Define custom getNode operator
function fetchNode<TNode>(getNodeFunction: GetNodeFunction) {
  return (observable: Observable<TNode>) =>
    observable.pipe(switchMap((response) => getNodeFunction(response)));
}

this.myService.getNodeById(response.parent_id).pipe(
  fetchNode((response) => this.myService.getNodeById(response.parent_id)),
  fetchNode((response) => this.myService.getNodeById(response.parent_id))
);

Answer 4

If you want to create a unique Rx.js operator, consider implementing one that integrates the necessary API calls within switchMap.

type GetNodeFunction<TNode = any, TResponse = any> = (
  response: TNode
) => Observable<TResponse>;

// Define custom getNode operator
function fetchNode<TNode>(getNodeFunction: GetNodeFunction) {
  return (observable: Observable<TNode>) =>
    observable.pipe(switchMap((response) => getNodeFunction(response)));
}

this.myService.getNodeById(response.parent_id).pipe(
  fetchNode((response) => this.myService.getNodeById(response.parent_id)),
  fetchNode((response) => this.myService.getNodeById(response.parent_id))
);

What is the best way to link together a varying amount of observables?

Answer №1

Answer №2

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