Nest js: class created by injection is shared across 2 services - dependency-injection

Question

In Nest Js, I have a module definition:
#Module({
imports: [ConfigModule.forRoot(), HelperModule],
providers: [
NEtheriumChainService,
NBinanceChainService,
NBitcoinChainService,
NChainServiceProvider,
{
provide: Web3,
useValue: new Web3(),
},
],
exports: [NChainServiceProvider],
})
export class NChainsModule {}
NEtheriumChainService and NBinanceChainService both accept a Web3 class in their constructor. I would have thought that this syntax would provide each service with its own Web3 instance, but they end up with the same instance of Web3 - effectively sharing it. How do I ensure that each service has its own dedicated Web3 instance?

Answer 1

With the release of nest.js 6.0, injection scopes were added. With this, you can choose one of the following three scopes for your providers:
SINGLETON: Default behavior. One instance of your provider is used for the whole application
TRANSIENT: A dedicated instance of your provider is created for every provider that injects it.
REQUEST: For each request, a new provider is created. Caution: This behavior will bubble up in your dependency chain. Example: If UsersController (Singleton) injects UsersService (Singleton) that injects OtherService (Request), then both UsersController and UsersService will automatically become request-scoped.
What you need is TRANSIENT
Usage
Either add it to the #Injectable() decorator:
#Injectable({ scope: Scope.TRANSIENT })
export class Web3 {}
Or set it for custom providers in your module definition:
{
provide: "Web3",
useClass: Web3,
scope: Scope.TRANSIENT,
}