- 9Overwrite a Service in a Component Subtree in Angular4m 41s
Overwrite a Service in a Component Subtree in Angular
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Angular's hierarchical dependency allows us to overwrite a global service with a different class implementation for just a given sub-tree of the entire component tree of your application.
In this lesson we will take a look how this works, by registering the service on the component's child injector.
why do I need to override PeopleService with WomanService into providers section? Couldn't I just provide the WomanService directly into the constructor?
Hey. Sure. You could directly use the WomenService in the WomenComponent of my example. The point here though is that in this way you can overwrite/specialize an entire subtree of your component tree. As I explain in the example towards the end, even if we place the <app-person> inside the template of the WomenComponent, it will also get the instance of our WomanService (though in its constructor it fetches a PersonService).
So without even changing the implementation of the component, we can still influence how it fetches data via this mechanism.
Ohh, now I see, the override will affect the current components and it's children that use the PeopleService. I've replayed the video and I saw that you did within WomanComponent. Thanks!
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Hi guess, in this case (useExisting will also work in addition to PersonService)
{ provide : PeopleService, useExisting: WomanService } will work, since WomanService is available from the parent app-module injector.