Resolve Guard: Proper way to resolve observable from Routes, if no data found

Question

resolve method in the example on the angular.io returns a promise or navigates the application to the specific route if no data was found.

resolve(route: ActivatedRouteSnapshot): Promise<any> {
let id = +route.params['id'];
return this.cs.getCrisis(id).then(crisis => {
  if (crisis) {
    return crisis;
  } else { // id not found
    this.router.navigate(['/crisis-center']);
    return false;
  }
});
}

suppose, that getCrisis function returning an observable:

resolve(route: ActivatedRouteSnapshot): Observable<any> {
  let id = +route.params['id'];
  return this.cs.getCrisis(id).take(1)
}

in case of observable. How do i know, that nothing is returned, as i am dealing with stream? what would be the best pattern to handle this case inside the resolve function?

I know, that i could user router.navigate method from the component, but would like to use the router resolve guard properly.

Answer 1

You might need to add .first() (needs to be imported) because currently the router waits for the observable to complete and that might not happen depending on what getCrisis() is doing:

resolve(route: ActivatedRouteSnapshot): Observable<any> {
  let id = +route.params['id'];
  return this.cs.getCrisis(id)
  .map(data => {
    if(data) {
      return crisis;
    } else {
      this.router.navigate(['/crisis-center']);
      return false;
    }
  })
  .first()
}