Is it possible for a factory provider to include optional dependencies?

Question

Is it possible for a factory provider to include optional dependencies?

As an illustration:

@NgModule ({
  providers: [ 
    { provide: MyService, 
      useFactory: (optionalDependency) => new MyService(optionalDependency)
      deps: [ANOTHER_DEP]
    }
})
class MyModule {}

Is it possible for useFactory to include optional dependencies?

angular typescript dependency-injection

Answer 1

Answer №1

As per the official documentation, here is a way you can achieve the following:

const Location = new InjectionToken('location');
const Hash = new InjectionToken('hash');

const injector = Injector.create([{
  provide: Hash,
  useFactory: (location: string) => `Hash for: ${location}`,
  // Use a nested array to define metadata for dependencies.
  deps: [[new Optional(), Location]]
}]);

expect(injector.get(Hash)).toEqual('Hash for: null');

For more information, visit https://angular.io/api/core/FactoryProvider#example

Answer 2

As per the official documentation, here is a way you can achieve the following:

const Location = new InjectionToken('location');
const Hash = new InjectionToken('hash');

const injector = Injector.create([{
  provide: Hash,
  useFactory: (location: string) => `Hash for: ${location}`,
  // Use a nested array to define metadata for dependencies.
  deps: [[new Optional(), Location]]
}]);

expect(injector.get(Hash)).toEqual('Hash for: null');

For more information, visit https://angular.io/api/core/FactoryProvider#example

Answer 3

Answer №2

I came across a clever solution:

class DependencyHandler {
  constructor(@Optional() @Inject(ANOTHER_DEP) public optionalDependency) {}
}

@NgModule ({
  providers: [ 
    { provide: AnotherService, 
      useFactory: (handler) => new AnotherService(handler.optionalDependency)
      deps: [DependencyHandler]
    }
})
class AnotherModule {}

Answer 4

I came across a clever solution:

class DependencyHandler {
  constructor(@Optional() @Inject(ANOTHER_DEP) public optionalDependency) {}
}

@NgModule ({
  providers: [ 
    { provide: AnotherService, 
      useFactory: (handler) => new AnotherService(handler.optionalDependency)
      deps: [DependencyHandler]
    }
})
class AnotherModule {}

Answer 5

Answer №3

After much deliberation, I have come up with a solution. Take a look at this:

@NgModule ({
  providers: [ 
    { provide: MyService, 
      useFactory: (optionalDep) => new MyService(optionalDep)
      deps: [[new Optional(), new Inject(SOME_DEP)]]
    }
})
class MyModule {}

Answer 6

After much deliberation, I have come up with a solution. Take a look at this:

@NgModule ({
  providers: [ 
    { provide: MyService, 
      useFactory: (optionalDep) => new MyService(optionalDep)
      deps: [[new Optional(), new Inject(SOME_DEP)]]
    }
})
class MyModule {}

Answer 7

Answer №4

Factories can incorporate a function into their processes.

Within TypeScript, decorators have the ability to be applied to various elements such as class declarations, methods, accessors, properties, and parameters.

As of now, decoration is only possible on classes and their members.

When discussing parameters here, it specifically refers to method parameters rather than standalone functions.

Due to this limitation, functions and their parameters cannot currently be decorated with tags like @Optional.

This restriction may evolve in the future due to language or specification updates.

It is worth noting that TypeScript's metadata feature, utilized by Angular through reflect-metadata, is primarily designed to operate on classes. Despite classes essentially being functions, this serves as the general conceptual framework.

Per the documentation, the deps array solely accepts provider tokens, which means indicating an optional dependency is not supported.

Addition of support for optional dependencies within factories would be advantageous. Consider submitting a feature request via a GitHub issue!

Answer 8

Factories can incorporate a function into their processes.

Within TypeScript, decorators have the ability to be applied to various elements such as class declarations, methods, accessors, properties, and parameters.

As of now, decoration is only possible on classes and their members.

When discussing parameters here, it specifically refers to method parameters rather than standalone functions.

Due to this limitation, functions and their parameters cannot currently be decorated with tags like @Optional.

This restriction may evolve in the future due to language or specification updates.

It is worth noting that TypeScript's metadata feature, utilized by Angular through reflect-metadata, is primarily designed to operate on classes. Despite classes essentially being functions, this serves as the general conceptual framework.

Per the documentation, the deps array solely accepts provider tokens, which means indicating an optional dependency is not supported.

Addition of support for optional dependencies within factories would be advantageous. Consider submitting a feature request via a GitHub issue!

Answer 9

Answer №5

Declaring an optional dependency for a factory provider is completely achievable.

export const OPTIONAL_SERVICE_PARAM = new OpaqueToken('optional_service_param');
export const optionalServiceParamDefault = 42;

To set the default value in your providers list, utilize a value provider.

@NgModule({
   providers: [
      {
          provide: OPTIONAL_SERVICE_PARAM, 
          useValue: optionalServiceParamDefault
      },
      {
          provide: MyService, 
          useFactory: (optParam) => new MyService(optParam)
          deps: [OPTIONAL_SERVICE_PARAM]
      }
})
export class Module {}

The service will make use of the default parameter value provided (which may be undefined), unless altered by the consumer later within the provider array.

The HttpModule sourced from @angular/http follows this same approach to supply the optional dependency RequestOptions to its services.

Answer 10

Declaring an optional dependency for a factory provider is completely achievable.

export const OPTIONAL_SERVICE_PARAM = new OpaqueToken('optional_service_param');
export const optionalServiceParamDefault = 42;

To set the default value in your providers list, utilize a value provider.

@NgModule({
   providers: [
      {
          provide: OPTIONAL_SERVICE_PARAM, 
          useValue: optionalServiceParamDefault
      },
      {
          provide: MyService, 
          useFactory: (optParam) => new MyService(optParam)
          deps: [OPTIONAL_SERVICE_PARAM]
      }
})
export class Module {}

The service will make use of the default parameter value provided (which may be undefined), unless altered by the consumer later within the provider array.

The HttpModule sourced from @angular/http follows this same approach to supply the optional dependency RequestOptions to its services.

Is it possible for a factory provider to include optional dependencies?

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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