typeORM in a nutshell.ts

// Firstly, we setup Database Connection
@Module({
  imports: [
    TypeOrmModule.forRoot({
      type: 'postgres',
      host: 'localhost',
      port: 5432,
      username: 'postgres',
      password: 'postgres',
      database: 'postgres',
      entities: [Cat],
      synchronize: true, // Sync the entities with the database every time the application runs
    }),
    CatsModule,
  ],
})

// Then you can define the data entity
@Entity()
export class Cat {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  name: string;

  @Column()
  breed: string;
}
// We can use repository design pattern which means each entity has its own repository.
// Here, we inject the catRepository into your service
export class CatsService {
  constructor(
    @InjectRepository(Cat)
    private catsRepository: Repository<Cat>,
  ) {}
  
  // Then you can use the injected repo to perform database operation
  this.catsRepository.find();
  this.catsRepository.save<Cat>(cat);