CODEWITHSUNDEEP
angulartypescriptdependency-injection
marcXandre
marcXandre

Reputation: 2432

How to inject a service in parent class without passing it in constructor? Angular 6

I will like to know how to inject a service with multiple dependencies inside an abstract class who will be extended by multiple classes.

In a more efficient way then passing it in all constructor!

I try to create static, but if the service is never instantiated by another, the singleton instance variable will never be assigned

Something like this: (Is just an example)

@Injectable({
  providedIn: 'root'
})
export class AnimalService {

  constructor(private http: HttpClient, private userService: UserService) {}

  countTotalInDB(type): number {
    return this.http.get(...);
  }

  getUserAnimals(userId: number) {
    return this.userService.getUser(userId).animals;
  }

}

abstract class Animal {

  constructor() {}

  public getTotalInDataBase(type): number {
    // How to get a instance of AnimalService ?
    return animalService.countTotalInDB(type);
  }

}

export class Cat extends Animal {

  constructor() {
    super();
  }

  public getTotalInDataBase(): number {
    return super.getTotalInDataBase('cat');
  }

}

export class Dog extends Animal {

  constructor() {
    super();
  }

  public getTotalInDataBase(): number {
    return super.getTotalInDataBase('dog');
  }

}

const doggo = new Dog();

console.log(doggo.getTotalInDataBase());

In this case, AnimalService will use HttpClient and UserService.

UserService will use a lot more services.

So how can I get a class instantiation who look like this const doggo = new Dog(); who will create/use/inject the AnimalService without passing it in all classes?

Upvotes: 3

Views: 2151

Answers (1)

marcXandre
marcXandre

Reputation: 2432

I finally find how to do this.

Following my example:

import { inject } from '@angular/core'; // Answer

@Injectable({
  providedIn: 'root'
})
export class AnimalService {

  constructor(private http: HttpClient, private userService: UserService) {}

  countTotalInDB(type): number {
    return this.http.get(...);
  }

  getUserAnimals(userId: number) {
    return this.userService.getUser(userId).animals;
  }

}

abstract class Animal {

  protected animalService: AnimalService; // Answer

  constructor() {
    this.animalService = inject(AnimalService); // Answer
  }

  public getTotalInDataBase(type): number {
    // How to get a instance of AnimalService ?
    return this.animalService.countTotalInDB(type);
  }

}

export class Cat extends Animal {

  constructor() {
    super();
  }

  public getTotalInDataBase(): number {
    return super.getTotalInDataBase('cat');
  }

}

export class Dog extends Animal {

  constructor() {
    super();
  }

  public getTotalInDataBase(): number {
    return super.getTotalInDataBase('dog');
  }

}

const doggo = new Dog();

console.log(doggo.getTotalInDataBase());

It works in my case, hope it will help you too!

Upvotes: 8

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