Entities

TypeORM entities map classes to tables via decorators: columns, relations, indexes, and lifecycle hooks. Persistence feels object-oriented but can mix domain behavior with storage mapping.

					@Entity()
export class Order {
  @PrimaryGeneratedColumn('uuid') id!: string;
  @Column() status!: string;
  @ManyToOne(() => Customer, (c) => c.orders) customer!: Customer;
}
				

On interviews: columns, relations, eager/lazy options, decorators, lifecycle hooks, migrations, metadata reflection costs.

Common pitfalls: decorators replacing constraints and indexes; lazy relations hiding async queries behind property access.

The trade-off is familiar OOP mapping versus hidden I/O in getters.

Checklist:

• Map constraints deliberately.
• Watch lazy relation behavior.
• Keep entity methods from hiding side effects.
• Separate entities from API DTOs.