Angular Material Paginator

I'm gonna be very specific with my question, hoping for an equally specific answer.

I've combed online, and the Angular docs on the subject is as vague for real life cases as asking you to pick a needle from the ocean. Ooh Angular docs...

What I have done so far

  <mat-paginator (page)="pageEvent = $event" #paginator [length]="pageLength" [pageSize]="pageSize" [pageSizeOptions]="pageSizeOptions">
  </mat-paginator>

And this in my component

  pageLength: number;
  pageSize: 5;
  pageSizeOptions = [5, 10, 25, 100];

and then I update the pageLength when the endpoint response is in like so:

  loadRequests() {
    this.busy = true;
    this.request_service.get_requests()
      .subscribe((res) => {
        console.log(res);
        this.requests = res['requests'];
        this.pageLength = this.requests.length; // let's assume length = 1000
      });
  }

The above renders renders the UI for the pagination nicely in the browser

The endpoint being consumed via .get_requests(), for the sake of simplicity, returns only 1000 fixed items.

Now, this is how I'm rendering my list at the moment:

<mat-card *ngFor="let request of requests">
  <mat-card-title> {{ request.title }}</mat-card-title>
</mat-card>

So with the above preamble, what steps are my left to complete to get pagination to work with this condition in mind:

The pagination doesn't keep going to endpoint to pull each list of items for each pageIndex.
After receiving the 1000 items at first hit from the endpoint, then pagination chunks this length of items up locally on the client side. No more API calls.

Solution

Let's assume you've loaded the response data (Array) in requests .

You can probably create a method that returns a set of data from the requests property using the splice method.

Therefore, on the API subscribe results, it can be handled like this for the first time load:

this.request_service.get_requests()
  .subscribe((res) => {
    this.pageLength = res['requests'].length;
    this.splicedData = res['requests'].slice(((0 + 1) - 1) * this.pageSize).slice(0, this.pageSize);
  });

where pageSize, has been defined in earlier on to a default value.

Then, anytime the user changes the mat-paginator component in the template, the pageChangeEvent is run. Template looks like this:

  <mat-paginator (page)="pageChangeEvent($event)" [length]="pageLength" [pageSize]="pageSize" [pageSizeOptions]="pageSizeOptions">
  </mat-paginator>

Then its corresponding component method is this.

 pageChangeEvent(event) {
    const offset = ((event.pageIndex + 1) - 1) * event.pageSize;
    this.splicedData = this.requests.slice(offset).slice(0, event.pageSize);
  }

Finally, your *ngFor can use the splicedData array to populate itself.

<mat-card *ngFor="let request of splicedData">
    <mat-card-title> {{ request.title }}</mat-card-title>
</mat-card>