How to use factory pattern correctly in nestjs - nestjs

Question

In Nestjs, I have a Module, which using useFactory to dynamically create class base on configValue
There is no dedicated service in that module, instead, it return a service that depends on config, therefore the DriverService1 and DriverService2 will construct together
export const createFactory = (config: IConfig):Provider<IService> => {
return {
provide: 'FACTORY',
useFactory: (service1: DriverService1, service2: DriverService2): IService => {
if (config.driver == 'DriverService1')
{
return service1;
}
else if (config.driver == 'DriverService2')
{
return service2;
}
throw new Error('not implemented')
},
inject: [ DriverService1, DriverService2 ],
}
};
#Module({})
export class MyModule {
static register(config?: IConfig): DynamicModule {
const factory = createFactory(config)
return {
module: MyModule,
providers: [
{
provide: 'CONFIG',
useValue: config,
},
DriverService1,
DriverService2,
factory
],
exports: [factory],
};
}
}
but im not sure is it a correct way to do that
or i should create a dedicated service in this module , e.g "MyModuleService", and then do the factory pattern inside the service? which the driver will only construct when it use
interface IDriver {
action1():void
action2():void
action3():void
}
class Driver1 implements IDriver{
public action1():void {
console.log("DriverService1 action1")
}
public action2():void {
console.log("DriverService1 action2")
}
public action3():void {
console.log("DriverService1 action3")
}
}
class Driver2 implements IDriver{
public action1():void {
console.log("DriverService2 action1")
}
public action2():void {
console.log("DriverService2 action2")
}
public action3():void {
console.log("DriverService2 action3")
}
}
export const createFactory = (config: IConfig):Provider<MyModuleSerice> => {
return {
provide: 'BROKER_FACTORY',
useFactory: (service:MyModuleSerice): MyModuleSerice => {
if (config.driver == 'Driver1')
{
service.setDriver(new Driver1());
}
else if (config.driver == 'Driver2')
{
service.setDriver(new Driver2());
}
else{
throw new Error('not implemented')
}
return service
},
inject: [ MyModuleSerice ],
}
};
#Module({})
export class MyModule {
static register(config?: IConfig): DynamicModule {
const facotry = createFactory(config)
return {
module: MyModule,
providers: [
{
provide: 'CONFIG',
useValue: config,
},
facotry
],
exports: [facotry],
};
}
}
#Injectable()
class MyModuleSerice {
protected driver:IDriver
constructor() {
}
public setDriver(driver:IDriver) {
this.driver = driver
}
public doSomething():void {
this.driver.action1()
this.driver.action2()
}
public doSomething2():void {
this.driver.action1()
this.driver.action3()
}
}

Answer 1

This is where providers come into play. You can create a custom provider that can handle this logic for you. See below.
https://docs.nestjs.com/fundamentals/custom-providers
Here's the example provided by NestJS that leverages a config file to create an instance of a service.
const configServiceProvider = {
provide: ConfigService,
useClass:
process.env.NODE_ENV === 'development'
? DevelopmentConfigService
: ProductionConfigService,
};
#Module({
providers: [configServiceProvider],
})
export class AppModule {}