What is the correct way to use forkJoin with an array containing nested arrays?

Question

Given the following array of objects, I need to collect a series of observables from calls to an endpoint

const data = [
    {
        body: [{ id: 1 }, { id: 2 }],
    },
    {
        body: [{ id: 3 }],
    },
];

const requests = data.map((entry) => entry.body.map((item) => this.someService.query(item.id).pipe(take(1))));

The result of this operation is similar to this

[ [ 1, 2 ], [ 3 ] ]

or

[[Observable, Observable], [Observable]]

In other cases I have passed to forkJoin flat arrays of observables and I get the results I require. But in this case with an array of nested arrays. What is the correct way to use forkJoin with an array containing nested arrays?

Picci · Accepted Answer · 2021-04-02 07:48:43Z

2

You may want to try something along these lines. See inline comments for details.

const data = [
  {
    body: [{ id: 1 }, { id: 2 }]
  },
  {
    body: [{ id: 3 }]
  }
];

forkJoin(
  // for each item of data create an Observable, which is the result of
  // executing the inner forkJoin
  data.map(entry =>
    // the inner forkJoin executes an array of Observables obtained by 
    // invoking someService.query on each item of the body
    forkJoin(entry.body.map(item => someService.query(item.id).pipe(take(1))))
  )
).subscribe(console.log);

Here a stackblitz to test it

answered Apr 2, 2021 at 7:48

Picci

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