Conditions are in an angular type provider with AOT

Question

Conditions are in an angular type provider with AOT

I am facing an issue with my Angular project that is compiled using AOT. I am trying to dynamically register a ClassProvider based on certain configurations. The simplified code snippet I am currently using is below:

const isMock = Math.random() > 0.5;

@NgModule({
  // ...
  providers: [
    { provide: MyServiceBase, useClass: (isMock) ? MyServiceMock : MyService },
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

However, the problem arises when I compile this code with AOT, as it always resolves to the same service instead of dynamically switching between services. It works as expected when compiled without AOT.

You can find the entire code example on GitHub here: https://github.com/vdolek/angular-test/tree/aot-conditioned-provider-problem. The behavior differs when running with ng serve and ng serve --aot.

Is there a way to achieve the dynamic provider registration behavior I need? I am aware of using a FactoryProvider, but that would involve duplicating service dependencies which I'd like to avoid.

javascript angular typescript decorator angular2-aot

Answer 1

Answer №1

To meet the dynamic requirements, utilize factory providers with the useFactory attribute.

I have cloned your repository and made changes to your app.module.ts file to make it compatible with AOT compilation.

Please modify app.module.ts as shown below:

export let myServiceFactory = () => {

  const isMock = Math.random() > 0.5;

  return isMock ? new MyServiceMock() : new MyService();
}; 

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule
  ],
  providers: [
    {provide: MyServiceBase, useFactory: myServiceFactory},
  ],
  bootstrap: [AppComponent]
})
export class AppModule {
}

If your service has dependencies on other services (which is likely), you can use the deps argument to inject these dependencies.

For instance, if MyServiceBase depends on MyService1 and MyService2, your factory function should be defined like this:

export let myServiceFactory = (service1:MyService1, service2:MyService2) => {

  const isMock = Math.random() > 0.5;

  return isMock ? new MyServiceMock(service1, service2) : new MyService(service1, service2);
};

Your provider declaration would then look like this:

providers: [
    {
       provide: MyServiceBase, 
       useFactory: myServiceFactory,
       deps: [MyService1, MyService2]
    },
]

Refer to this guide for more details on Angular dependency injection methods.

Answer 2

To meet the dynamic requirements, utilize factory providers with the useFactory attribute.

I have cloned your repository and made changes to your app.module.ts file to make it compatible with AOT compilation.

Please modify app.module.ts as shown below:

export let myServiceFactory = () => {

  const isMock = Math.random() > 0.5;

  return isMock ? new MyServiceMock() : new MyService();
}; 

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule
  ],
  providers: [
    {provide: MyServiceBase, useFactory: myServiceFactory},
  ],
  bootstrap: [AppComponent]
})
export class AppModule {
}

If your service has dependencies on other services (which is likely), you can use the deps argument to inject these dependencies.

For instance, if MyServiceBase depends on MyService1 and MyService2, your factory function should be defined like this:

export let myServiceFactory = (service1:MyService1, service2:MyService2) => {

  const isMock = Math.random() > 0.5;

  return isMock ? new MyServiceMock(service1, service2) : new MyService(service1, service2);
};

Your provider declaration would then look like this:

providers: [
    {
       provide: MyServiceBase, 
       useFactory: myServiceFactory,
       deps: [MyService1, MyService2]
    },
]

Refer to this guide for more details on Angular dependency injection methods.

Answer 3

Answer №2

It seems that using a factory is the only option, as pointed out by @jeanpaul-a. However, managing dependencies in this approach may not be very straightforward. One alternative solution could be utilizing the Injector. A possible implementation could look like this:

@NgModule({
  imports:      [ BrowserModule, FormsModule ],
  declarations: [ AppComponent, HelloComponent ],
  providers: [
    Dep1Service,
    Dep2Service,
    { provide: MyServiceBase, useFactory: createService, deps: [Injector] }
  ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

export function createService(injector: Injector) {
  const isMock = Math.random() > 0.5;
  if (mock) {
    return new MyService1(injector.get(Dep2Service));
  } else {
    return new MyService2(injector.get(Dep1Service));
  }
}

Another approach you can take is to define MyServiceBase as an interface and utilize InjectionToken. You can explore a live example here (please note that the class names are different).

Answer 4

It seems that using a factory is the only option, as pointed out by @jeanpaul-a. However, managing dependencies in this approach may not be very straightforward. One alternative solution could be utilizing the Injector. A possible implementation could look like this:

@NgModule({
  imports:      [ BrowserModule, FormsModule ],
  declarations: [ AppComponent, HelloComponent ],
  providers: [
    Dep1Service,
    Dep2Service,
    { provide: MyServiceBase, useFactory: createService, deps: [Injector] }
  ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

export function createService(injector: Injector) {
  const isMock = Math.random() > 0.5;
  if (mock) {
    return new MyService1(injector.get(Dep2Service));
  } else {
    return new MyService2(injector.get(Dep1Service));
  }
}

Another approach you can take is to define MyServiceBase as an interface and utilize InjectionToken. You can explore a live example here (please note that the class names are different).

Conditions are in an angular type provider with AOT

Answer №1

Answer №2

Similar questions

Update the message displayed in the user interface after the view has been fully rendered in an Express application, following the execution of asynchronous

Displaying the information fetched using axios on the screen using node.js

Attempting to adjust the width of a text animation loaded with jQuery using Textillate, but encountering difficulties

The WebView.HitTestResult method is currently only receiving <img src> elements and not <a href> elements

Error encountered when utilizing Meteor in conjunction with TypeScript

What is the best approach to updating multiple rows instead of just the first row using the update button located on both sides using PHP and AJAX?

The issue with Angular 4 imports not refreshing in a .less file persists

Concealing overflow in a sticky container when a fixed child element is present

Having trouble getting Angular-UI-Select to work with a basic variable on $scope?

Is it possible for Node.js to not automatically restart the server when modifying .js files?

The specified "ID" type variable "$userId" is being utilized in a positional context that is anticipating a "non-null ID" type

Clicking on Rows in DataTables: Enhancing

The function has been called but it did not return a

Arrange pictures and div elements in a horizontal layout

Tips for extracting key values from an array of objects in Typescript

AngularJS Splice Function Used to Remove Selected Items from List

Greetings, Angular2 application with TypeScript that showcases the beauty of the world

Encountering difficulties setting cookies within the app router in Next.js

The specified 'IArguments' type does not qualify as an array type

Discovering the worth of specific selections in a dropdown menu