spring-data-jpa

Spring Data Jpa

Use When

• Working with JPA entities, repositories, projections, or N+1 prevention
• Spring Boot code generation or refactor where agent defaults would be wrong

Workflow

1. Confirm the change matches this skill's domain triggers before coding.
2. Follow the domain guide conventions and gotchas below — not generic Spring Boot defaults.
3. Apply project-specific response envelopes, DTO boundaries, and dependency injection rules.
4. Validate with targeted tests (slice, integration, or contract as appropriate).
5. Capture evidence before merge: tests, migration notes, or observability proof.

Required Checks

• Constructor injection used; no @Autowired field injection on new code
• Controllers return DTOs/envelopes — never raw JPA entities
• Business logic stays in @Service layer, not controllers or repositories
• Error handling uses project-standard envelope or RFC 9457 ProblemDetail

Domain Guide

Entity Conventions

@Entity
@Table(name = "orders")
@Getter
@NoArgsConstructor(access = AccessLevel.PROTECTED) // JPA requires no-arg, hide from callers
public class Order {

    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    @Column(updatable = false, nullable = false)
    private UUID id;

    @Column(nullable = false)
    private String customerEmail;

    @Enumerated(EnumType.STRING) // always STRING, never ORDINAL
    @Column(nullable = false)
    private OrderStatus status;

    @OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<OrderItem> items = new ArrayList<>();

    @CreationTimestamp
    @Column(updatable = false)
    private Instant createdAt;

    @UpdateTimestamp
    private Instant updatedAt;

    // Static factory, not public constructor
    public static Order create(String customerEmail) {
        Order order = new Order();
        order.customerEmail = customerEmail;
        order.status = OrderStatus.PENDING;
        return order;
    }

    // Behavior on entity, not in service
    public void addItem(Product product, int quantity) {
        items.add(OrderItem.create(this, product, quantity));
    }
}