Optional Registration using the ConfigModule

[jmcdo29]

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

There arises occasions where we might want to allow for registering a module optionally, I see this come up on the Discord server every now and again. Like running the CronModule in only one running instance based on the env variables, or setting up the serve static in a single instance.

Describe the solution you'd like

I'd like to propose a new static method on the ConfigModule, something like optionallyRegisterModule that takes in the module to optionally register, and the environment variable that should be checked against if the module should be registered, or a method that returns a boolean for the same reason. If the valueof the key is falsy, or the method returns false, the new method should return a new NoopModule which has no imports, exports, providers, or controllers.

This method would be an async method that await ConfigModule.envVariablesLoaded and then check against process.env[key] to ensure that we can properly wait for the environment variables to be loaded and then react accordingly.

Teachability, documentation, adoption, migration strategy

We mention it in the docs and possibly make a blog article on it

What is the motivation / use case for changing the behavior?

Optionally registering modules, as described above :)

I'm happy to work on this as well if we like the idea of it.

[micalevisk]

can you show some code snippet on how it would looks like from consumer side?

[jmcdo29]

@Module({
  imports: [
    ConfigModule.forRoot(),
    ConfifgModule.optionallyRegisterModule(
      ScheduleModule.forRoot(),
      'USE_CRON'
    )
  ],
  ...
})
export class AppModule {}

OR

@Module({
  imports: [
    ConfigModule.forRoot(),
    ConfifgModule.optionallyRegisterModule(
      ScheduleModule.forRoot(),
      () => JSON.parse(process.env.USE_ENV)
    )
  ],
  ...
})
export class AppModule {}

[micalevisk]

I wonder if it couldn't be something that works on top of ConfigService:

@Module({
  imports: [
    ConfigModule.forRoot(),
    ConfigModule.registerModule({
      module: ScheduleModule.forRoot(),
      when: (configService: ConfigService) =>
        configService.get('USE_ENV') == true
    })
  ],
  ...
})
export class AppModule {}

[jmcdo29]

Hmmm, I'm not quite sure how feasible that would be, as injecting a provider is usually for module configuration, not module registration, y'know? But as imports can have async values, we can make use of the existing method for waiting for process.env to be loaded and return the correct module. I do like the registerModule with the object rather than the two parameters though

[kamilmysliwiec]

So basically you're suggesting that we could expose this helper type out of the box, as part of the @nestjs/config package:

export class ConditionalModule {
  static async registerWhen(moduleToRegister, condition) {
    await ConfigModule.envVariablesLoaded();
    return condition(process.env) 
         ? { module: ConditionalModule, imports: [moduleToRegister] 
         : { module: ConditionalModule, imports: [] }
  }
}

Example

imports: [ConditionalModule.registerWhen(ScheduleModule.forRoot(), ({ USE_CRON }) => ...)]

[jmcdo29]

@kamilmysliwiec yep, that's generally it. Figured we'd make it a part of this package as it's very closely tied to the module

[kamilmysliwiec]

This would make a lot of sense indeed. Would you like to create a PR for this?

[jmcdo29]

Absolutely. I'll work on it this week

[jmcdo29]

Let's track this here