[Backend] Evaluierung - Integration von mehreren Datenbanken

[dschlarmann]

Short:
In order to provide an flexible approach for answering geo-related queries, the backend should be able to integrate and request different database-instances at the same time.

Details:
Quering multiple database at the same time make the backend more flexible. There might be the use case, that the service-instance provider hosts the service-instance for multiple customers, where each customer organises the the data in a separate database. Those databases could have a different databasesystem, datamodels and could be hosted in another datacenter or even cloud service.

ToDo:

• Please evaluate the the integration of multiple database(systems). This includes:
  • Connection-Parametes. Is it possible to define ConnectionPools separately?
• Please note some information how a configuration could be set up.
  • This is needed because a unique identifier between "topic" and database table is needed.
    • ❗ The databasetable name itself is not unique

Some (random) reading:

• Sequelize: https://sequelize.org/
  • Using multiple databases: https://www.unetiq.com/blog-posts/using-multiple-databases-with-nodejs-and-sequelize
• node-postgres: How I can have two different connection pools for two different databases? brianc/node-postgres#975
• NestJS: https://docs.nestjs.com/techniques/database#multiple-databases

[artmarks]

we can use the integrated possibilites of our ORM-framework typeORM or sequelizer to realize multiple database connections, multiple connection pool, timeouts and other common connection parameters.
Nest databases

Mutliple databases can ne set like this:

const defaultOptions = {
  type: 'postgres',
  port: 5432,
  username: 'user',
  password: 'password',
  database: 'db',
  synchronize: true,
};

@Module({
  imports: [
    TypeOrmModule.forRoot({
      ...defaultOptions,
      host: 'user_db_host',
      entities: [User],
    }),
    TypeOrmModule.forRoot({
      ...defaultOptions,
      name: 'albumsConnection',
      host: 'album_db_host',
      entities: [Album],
    }),
  ],
})

and can be integrated in a service via Injectables:

@Injectable()
export class AlbumsService {
  constructor(
    @InjectDataSource('albumsConnection')
    private dataSource: DataSource,
    @InjectEntityManager('albumsConnection')
    private entityManager: EntityManager,
  ) {}
}