Multiple databases from an asynchronous config service? - nestjs

Question

NestJS documentation describes how to define multiple databases:
https://docs.nestjs.com/techniques/database#multiple-databases
As well as using a database config service for asynchronous configuration:
https://docs.nestjs.com/techniques/database#async-configuration
Is it possible to define multiple databases from an async config service?
Experimentally I tried returning an array of options from my service:
class TypeOrmConfigService implements TypeOrmOptionsFactory {
createTypeOrmOptions() {
return [
{ ... },
{ ... }
];
}
}
but no luck with this approach.

Answer 1

It looks like for each connection you want to have you will need to create a separate configuration instance. What I might suggest would be some sort of factory that takes in a name, and maybe the config key for the database connection, then using those in the factory to help return the expected values. So the docs have a factory like
TypeOrmModule.forRootAsync({
imports: [ConfigModule],
useFactory: async (configService: ConfigService) => ({
type: 'mysql',
host: configService.getString('HOST'),
port: configService.getString('PORT'),
username: configService.getString('USERNAME'),
password: configService.getString('PASSWORD'),
database: configService.getString('DATABASE'),
entities: [__dirname + '/**/*.entity{.ts,.js}'],
synchronize: true,
}),
inject: [ConfigService],
});
You could create a similar factory along the lines of
const typeOrmFactory = (
configName: string,
entities: string[],
databaseName?: string
) => (configService: ConfigService): TypeOrmModuleOptions => ({
type: 'postgres', // whatever you use
url: configService.get(configName), // dynamically change which connection you're working with based on the factory input
name: databaseName || 'default',
synchronize: true,
entities // path to the entity/entities you are working with
});
Now in your app.module you can use the factory like so
#Module({
imports: [
TypeOrmModule.forRootAsync({
imports: [ConfigModule],
useFactory: typeOrmFactory('DATABASE_URL', ['some/path.ts']),
inject: [ConfigService]
}),
TypeOrmModule.forRootAsync({
imports: [ConfigModule],
useFactory: typeOrmFactory('DATABASE_URL_2', ['some/other/path.ts'], 'secondaryDatabase'),
inject: [ConfigServce]
],
})
export class AppModule {}
Make sure you tell Typescript that you are returning the type TypeOrmModuleOptions otherwise it tells you that the functions are not compatible. You can also save most of the configs in the config service and environment variables if you would like.