Executing resolvers one after the other in Angular 2+

Question

Given the following route:

path: '',
component: MyComponent,
resolve: {
    foo: FooResolver,
    bar: BarResolver
}

Is there any way of telling angular to execute the first resolver FooResolver, and only execute the second resolver BarResolver once the first one has finished?

Answer 1

Resolvers are resolved in parallel. If Foo and Bar are supposed to be resolved in series they should be a single FooBar resolver. If they are supposed to be used by themselves in other routes, FooBar can wrap Foo and Bar resolvers:

class FooBarResolver implements Resolve<{ foo: any, bar: any }> {
  constructor(
    protected fooResolver: FooResolver,
    protected barResolver: BarResolver
  ) {}

  async resolve(route): Promise<{ foo: any, bar: any }> {
    const foo = await this.fooResolver.resolve(route);
    const bar = await this.barResolver.resolve(route);

    return { foo, bar };
  }
}

FooBar should be aware of the fact if it is a promise or an observable that is returned from Foo and Bar in order to resolve them properly. Otherwise additional safety device should be added, like await Observable.from(this.fooResolver.resolve(route)).toPromise().

FooBar and Foo or Bar shouldn't appear within same route because this will result in duplicate resolutions.