Include the providers after declaring the AppModule

Question

Include the providers after declaring the AppModule

When it comes to Angular 2+, providers are typically registered in the following manner:

// Using the @NgModule decorator and its metadata
@NgModule({
  declarations: [...],
  imports: [...],
  providers: [<PROVIDERS GO HERE>],
  bootstrap: [...]
})
export class AppModule { }

However, I am interested in setting up application-scoped providers separately from this declaration location.

My current situation involves utilizing NSwag to automatically create service clients for my entire Web API, and I wish to dynamically add these generated service clients as providers. The challenge lies in finding a way to accomplish this task, especially given that @NgModule is an attribute that applies to the AppModule class itself.

Do you happen to know if achieving this separation of concern is actually feasible?

javascript angular typescript angular-providers nswag

Answer 1

Answer №1

Every DI provider must be included in the module during compile time.

Angular dependency injection operates using Typescript type symbols / tokens, making it impossible to achieve the same functionality in Javascript post compilation.

To add a provider dynamically at compile time, you can follow this example:

import { Load, SomeToken } from '../someplace';


@NgModule({
  declarations: [...],
  imports: [...],
  providers: [
    {
      provide: SomeToken,
      useValue: Load(someVariable)
  ],
  bootstrap: [...]
})
export class AppModule { }

and then define the Load function and token elsewhere:

export const SomeToken = new OpaqueToken<any>('SomeToken');

export const Load = (someVariable) => {
  // logic to return an @Injectable here. Variable provided could be something like an environment variable, but it has to be exported and static
}

This method limits the need for information to be known during compile time. An alternative approach is to either globally import all required providers throughout the app regardless of circumstance and lazily load components with the necessary provider injected when needed, or create a provider that can perform the logic irrespective of dynamic criteria. One suggestion is to create another service that utilizes the first service and resolves things based on dynamic criteria.

If only API information is required (such as URLs), one option is to fetch URL information from a config.json file or through an API call, and inject those values into the service so the calls and tokens remain consistent but with different values. For more details on achieving this, refer to this link.

Answer 2

Every DI provider must be included in the module during compile time.

Angular dependency injection operates using Typescript type symbols / tokens, making it impossible to achieve the same functionality in Javascript post compilation.

To add a provider dynamically at compile time, you can follow this example:

import { Load, SomeToken } from '../someplace';


@NgModule({
  declarations: [...],
  imports: [...],
  providers: [
    {
      provide: SomeToken,
      useValue: Load(someVariable)
  ],
  bootstrap: [...]
})
export class AppModule { }

and then define the Load function and token elsewhere:

export const SomeToken = new OpaqueToken<any>('SomeToken');

export const Load = (someVariable) => {
  // logic to return an @Injectable here. Variable provided could be something like an environment variable, but it has to be exported and static
}

This method limits the need for information to be known during compile time. An alternative approach is to either globally import all required providers throughout the app regardless of circumstance and lazily load components with the necessary provider injected when needed, or create a provider that can perform the logic irrespective of dynamic criteria. One suggestion is to create another service that utilizes the first service and resolves things based on dynamic criteria.

If only API information is required (such as URLs), one option is to fetch URL information from a config.json file or through an API call, and inject those values into the service so the calls and tokens remain consistent but with different values. For more details on achieving this, refer to this link.

Include the providers after declaring the AppModule

Answer №1

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