Access parent Route params with Angular's Router

Angular Tagged in Angular Aug 22, 2017 2 mins read by Todd Motto

With the router/URL being an application’s “source of truth”, we need to be able to access parts of the URL for data purposes, such as grabbing a dynamic :id property from the URL, passing it into a service and bringing back the relevant data. Let’s look at how we can use Angular’s Observable-driven Router so get automatic updates when a parent route changes.

Scenario

I’m currently working on building out Ultimate Angular’s platform, and as such have these routes (in the URL, not my routing definitions) - with us assuming 1234 is our dynamic :id:

/admin/courses/1234/metadata
/admin/courses/1234/curriculum
/admin/courses/1234/prices
/admin/courses/1234/coupons

What this structure allows me to do is click a particular “course” from /admin/courses, and be navigated to the /1234/metadata view where I can edit the course’s name, author and so forth.

Parent Route Param subscriptions

What I needed to do is (based on the parent’s param), is go off to my Store and fetch the appropriate course I’m viewing.

First let’s walk through the routes:

// routes
export const ROUTES: Routes = [
  {
    path: '',
    canActivate: [CoursesGuard],
    component: CoursesComponent,
  },
  {
    path: ':id',
    canActivate: [CoursesGuard],
    component: CourseComponent,
    children: [
      { path: '', redirectTo: 'metadata', pathMatch: 'full' },
      { path: 'metadata', component: CourseMetadataComponent },
      { path: 'curriculum', component: CourseCurriculumComponent },
      { path: 'prices', component: CoursePricesComponent },
      { path: 'coupons', component: CourseCouponsComponent },
    ],
  },
];

When my path is '', I use the CoursesComponent, and when we navigate to (for example /courses/1234/) - the CourseComponent is loaded (non-plural version). At this point, this CourseComponent is simply a container which renders a <router-outlet>. Once we hit that :id, we’re directed to the first child route, metadata.

Let’s look what’s inside the CourseMetadataComponent, paying attention to ActivatedRoute and the course$ Observable:

// ... other imports etc.
import { ActivatedRoute } from '@angular/router';

@Component({
  selector: 'course-metadata',
  styleUrls: ['course-metadata.component.scss'],
  template: `
    <div class="course-metadata">
      {{ course$ | async | json }}
    </div>
  `,
})
export class CourseMetadataComponent {
  course$ = this.router.parent.params.switchMap(params => {
    return this.store
      .select(getCoursesState)
      .map((courses: any) => courses.courses.find(course => course._id === params.id));
  });

  constructor(
    private router: ActivatedRoute,
    private store: Store<CoursesState>
  ) {}

}

At this point, the switchMap is given the params Object, which as you can see is driven from this.router.parent.params - which you may have used this before (without the .parent):

// not the parent, it's the current param
course$ = this.router.params.switchMap(params => {
  // do something with local "params"
});

So what is params when we do this?

course$ = this.router.parent.params.switchMap(params => {
  // params = { id: 1234 }
});

In my case, with /admin/courses/1234/metadata, the params on the parent are in fact an Object containing { id: 1234 }.

This means from */1234/metadata, */1234/curriculum, */1234/prices and */1234/coupons - I have access to 1234 for passing off into ngrx/store to fetch the correct course. The courses are always available when hitting these routes because I’m using:

{
  canActivate: [CoursesGuard];
}

This way, it’ll make an API request if ngrx/store doesn’t contain any courses, otherwise it’ll pass the API request and head straight across to the correct course, pulling the data from the pre-populated store.

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