This is how I build a class to connect to my mongoDb before. As you can see, I connect to the Db and also I create a gfs, which uses mongo.GridFSBucket. This is needed to handle image files.

export default class Db {
  constructor (uri, callback) {
    const mongo = process.env.MONGO || 'mongodb://localhost:27017'
    this.mongodb = 'data'
    this.db = null
    this.gfs = null
    this.connection = MongoClient.connect(mongo)
    return this
  }

  async connect (msg) {
    if (!this.connected) {
      try {
        this.connection = await this.connection
        this.connection = this.connection.db(this.mongodb)
        this.gfs = new mongo.GridFSBucket(this.connection)
        this.connected = true
      } catch (err) {
        console.error('mongo connection error', err)
      }
    }
    return this
  }
}

No I switched the backend to a nestJS application and I don't know how to create the gfs instance in a module:

  @Module({
    providers: [
      {
        provide: 'DATABASE_CLIENT',
        useFactory: () => ({ client: null })
      },
      {
        provide: 'DATABASE_CONNECTION',
        inject: ['DATABASE_CLIENT'],
        useFactory: async (dbClient): Promise<Db> => {  

          const mongo = 'mongodb://localhost:27017'
          const options = {}
          const client = new MongoClient(mongo, options)
  
          try {
            await client.connect()
            dbClient.client = client
            const db = client.db('data')
            // How to create a GridFSBucket instance?
            // dbClient.gfs = new GridFSBucket(db)
            return db
          } catch (error) {
            console.error(error)
          }
        }
      }
    ],
    exports: ['DATABASE_CONNECTION', 'DATABASE_CLIENT']
  })
  export class DatabaseModule {
    constructor(@Inject('DATABASE_CLIENT') private dbClient) {}
  
    onApplicationShutdown(signal) {
      if (signal) console.log(signal + ' signal recieved') // e.g. "SIGINT"
    }
  }

Also this gfs should be returned only if needed. The DatabaseModule is used like this in any other module, which needs db connection:

@Module({
    imports: [DatabaseModule],
    providers: [PhotosService, PhotosResolvers]
})
export class PhotosModule {}

But not every module needs the gfs instance, so I need to pass something like useGfs = true. How do I pass a parameter?