Proper way to initialize config

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[ ] Regression [ ] Bug report [ ] Feature request [x] Documentation issue or request [ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

There is nothing but a short snippet about a “configServiceProvider” in the documentation:

const configServiceProvider = {
  provide: ConfigService,
  useClass: DevelopmentConfigService,
};

@Module({
  components: [configServiceProvider],
})

Expected behavior

One article describing how to properly create a ConfigService provider which loads variables from the .env file, including validation (for example: is port actually a number between 1 and 65535?) and usage in other components.

It could easily be added to one of the examples showing how to pass database credentials for example.

[kamilmysliwiec]

Creating new abstractions like modules dependent on providers directly might create too much mess. However, I fully understand your concerns, the possibility to pass options asynchronously is a very essential thing. Thus, I just published new versions of both @nestjs/typeorm and @nestjs/mongoose modules. They expose forRootAsync() method now, which give various ways to initialize the configuration object.

1. Use factory

MongooseModule.forRootAsync({
  useFactory: () => ({
    uri: 'mongodb://localhost:27017/test',
  }),
}),

Obviously, our factory behaves like every other one (might be async and is able to inject dependencies inject).

MongooseModule.forRootAsync({
  imports: [ConfigModule],
  useFactory: async (configService: ConfigService) => ({
    uri: configService.getString('MONGO_URL'),
  }),
  inject: [ConfigService],
}),

2. Use class

MongooseModule.forRootAsync({
  useClass: MongooseConfigService,
})

Above construction will instantiate MongooseConfigService inside MongooseModule and will leverage it to create options object.

class MongooseConfigService implements MongooseOptionsFactory {
  createMongooseOptions(): MongooseModuleOptions {
    return {
      uri: 'mongodb://localhost:27017/test',
    };
  }
}

3. Use existing

MongooseModule.forRootAsync({
  imports: [ConfigModule],
  useExisting: ConfigService,
}),

It works the same as useClass with one critical difference - MongooseModule will lookup imported modules to reuse already created ConfigService, instead of instantiating it on its own.

The internal implementation is quite simple. Everyone who is interested in that should check the repositories to see how it is achieved underneath.

[sebastianvidales]

@cdiaz thanks. And now how do I pass a config variable to dynamic module in the forRoot() method?

import { Module } from '@nestjs/common';
import { MongooseModule } from '@nestjs/mongoose';

@Module({
  imports: [MongooseModule.forRoot(this.config.mongoUri)],
})
export class ApplicationModule {}