$ npm i --save @hungtcs-box/nest-nedb nedb
$ npm i --save-dev @types/nedb

import { Model } from '@hungtcs-box/nest-nedb';

export class UserModel extends Model {
  username?: string;

}

import { UserModel } from './models/user.model';
import { NedbModule } from '@hungtcs-box/nest-nedb';

@Module({
  imports: [
    PasswdModule,
    NedbModule.forFeature([
      {
        model: UserModel,
        indexes: {
          username: {
            unique: true,
          },
        },
      },
    ]),
  ],
  exports: [
    UsersService,
  ],
  providers: [
    UsersService,
  ],
  controllers: [
    UsersController,
  ],
})
export class UsersModule {

}

import { NedbModule } from '@hungtcs-box/nest-nedb';

@Module({
  imports: [
    NedbModule.forRoot(`path/to/your/database/file`),
  ],
  controllers: [
    AppController,
  ],
})
export class AppModule {

}

@Injectable()
export class UsersService {

  constructor(
      @InjectDatastore(UserModel) private readonly dataStore: DataStore<UserModel>) {

  }

}