Angular: How to get parameter from httpClient request and use in looping over the same request-CodePudding

So I have a method that get tree parents by id from the server

getParentById(id:string):return httpClient

I want to loop over this method and take the parentId returned from this call and put it back as a parameter to get the children, I only have the very first parentId so i pass it in the first call;

this.parentId ='123'

for(let i =0;i<arr.length;i  ){
   this.getNodeById(this.parentId).subscribe(res =>{

     this.parentId = res.parentId; 

    // I am trying to append the parent id I have, so in the next iteration of th loop, the 
      parent id is updated
  })
}

The problem is that the very first parentId value is not changing and all the requests are sent with the same parentId ,How can I solve this issue ?

CodePudding user response：

The problem is most likely that you are subscribing to this function:

this.getNodeById(this.parentId)

x arr.length times really fast.

And only then your values arrive, all for the same id.

CodePudding user response：

The best solution for you is to use EXPAND, an rxjs operator for recursive calls

import { from, EMPTY } from 'rxjs';
import { expand, tap} from 'rxjs/operators';

this.getNodeById(this.parentId).pipe(
  tap(res => {
      // do something on success
 }),
 expand((res) => res.parentId  // call getNodeById if you have a parentId otherwise return EMPTY
     ? this.getNodeById(res.parentId)
     : EMPTY;
 )
 ).subscribe(console.log)