Angular 6 - creating a (non root) module scoped service

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As far as i know until angular 6 , all the @Ngmodule providers where registered on the root injector and were served in the main bundle even if only lazy loaded modules used them.

The only only exception to this was if we wanted to create a non singleton services in a component level.

I want to create a singleton service which will be visible only to a specific module (not to the root module), and as a result of that will not be served in the main eagerly loaded bundle.

In saw that in angular 6 the module will no longer need to refer the service via the "providers" , but rather the service will now refer to the module.

This can be done by the @Injectable annotation and the provideIn attribute.

I didn't find a good and clear example of how can i add a module name which is not 'root', something like this:

@Injectable({ provideIn: <MyLocalModule>})
export class SimpleServiceForLocalUseOnly { […] }

There seems to be some issues regarding circular dependency if we follow this setup according to the official docs:

import { Injectable } from '@angular/core';
import { HeroModule } from './hero.module';
import { HEROES }     from './mock-heroes';

@Injectable({
  // we declare that this service should be created
  // by any injector that includes HeroModule.

  providedIn: HeroModule,
})
export class HeroService {
  getHeroes() { return HEROES; }
}

You can either ignore the warnings that the compiler raises due to circular dependency between the Module, Service and Component. Or, fallback to the previous methods used in Angular 5.

Register service as providers in lazy loaded module, note that you should not import lazy loaded modules in your root app module:

@NgModule({
  imports: [
    RouterModule.forChild([{ path: '', component: LazyComponent }]),
  ],
  declarations: [
    LazyComponent
  ],
  providers: [YourServiceHere]
})
export class LazyLoadedModule { }

Providing dependencies in modules, Create a Feature Component � 4. Add Services � 5. Add In-app Navigation � 6. Most of the time, these dependencies are services that you create and the local instance of the service, not the instance in the root application injector. Generally, provide services the whole app needs in the root module and scope services� Include the service in the AppModule or in a module that is only imported by the AppModule; Using providedInlink. Beginning with Angular 6.0, the preferred way to create a singleton service is to set providedIn to root on the service's @Injectable() decorator. This tells Angular to provide the service in the application root.

To provide a service in a specific module using the newer syntax you just do something like this:

import { Injectable } from "@angular/core";
import { YourModule } from "path/to/your.module";

@Injectable({
    providedIn: YourModule
})
export class SomeModuleScopedService {}

reference: https://angular.io/guide/providers#providedin-and-ngmodules

Angular 6 - creating a (non root) module scoped service, I want to create a singleton service which will be visible only to a specific module (not to the root module), and as a result of that will not be served in the main� Creating Service Class. Our service will contain the create, read, update and delete methods for a demo task management app. To create an Angular Service class, you need to run the following command via Angular CLI. ng generate service crud. Above command creates the following files in the src/app folder.

I got this to work by creating an intermediate module that holds only the service.

import { Injectable } from '@angular/core';
import { HeroServiceModule } from './hero.service.module';

@Injectable({
  providedIn: HeroServiceModule,
})
export class HeroService {
}

You don't need much in that module:

@NgModule({
  imports: [ CommonModule ]
})
export class HeroServiceModule {}

Then your regular module imports the service module:

@NgModule({
...
  imports: [
...
     HeroServiceModule
  ]
})
export class HeroModule {}

Then you can lazy-load HeroModule as normal. This eliminates all the circular dependencies.

Understanding provider scope in Angular | by J Stepanyan, The second way (more preferred in Angular 6) is to… When you provide the service at the root level, Angular creates a single, shared instance of Now let's create a feature module (not lazy ) and also provide VoteService Root Module. The Angular requires one module to be loaded as the application starts. We call this as root module. The root module loads the root component and all other modules. The root module is conventionally called as AppModule and created under the /src/app.folder

A detailed look at Angular's 'root' and 'any' provider scopes, Gives you a separate service instance per lazy module (+ one for 'root') In Angular 6 providedIn property was added to providers, to make services It means if you create a service but do not use it, in your application the� In this case, providedIn: 'root' specifies that Angular should provide the service in the root injector. Provider scope link When you add a service provider to the root application injector, it’s available throughout the app. Additionally, these providers are also available to all the classes in the app as long they have the lookup token.

Total Guide To Angular 6+ Dependency Injection — providedIn vs , If we wanted to create our service without Angular DI mechanism we would have Modules can be providedIn the 'root' or in any of the available inside of @ Component or @Directive to scope service only for the particular� In this article and upcoming article, we will discuss performing CRUD operations in Angular 6 i.e. Creating, Reading, Updating and Deleting in Angular 6 with simple examples. We will also discuss about the Angular 6 Project setup, apply Routing, create service to read and display data, create forms for create, update and delete data.

Angular creates injectors for you as it executes the app, starting with the root injector that it creates during the bootstrap process. A provider tells an injector how to create the service. You must configure an injector with a provider before that injector can create a service (or provide any other kind of dependency).

Comments
  • When i do it i get: WARNING in Circular dependency detected: HeroService -> HeroModule -> HeroComponent -> HeroService
  • it could be a problem with the Angular library itself, basically cause this setup requires circular imports of service, module and component. If it is just a WARNING and your app is working then I think it is safe to ignore. Or you could just not use the way to set up module-scoped services. Just set up the service in the providers array in your lazy loaded module.
  • But my initial purpose was not to include this service in the main bundle, adding it to the modules providers array will end up with this result.
  • are you lazy loading your module? From my understanding, services registered in lazy loaded modules are lazily loaded as well.
  • Yes, this module is lazy loaded, and services which are registered on the module's "providers" are added to the root injector and not being lazy loaded (check you're main bundle and see). As far as i understand in angular 6 it was changed (in the 2nd link there is a good cover of this).