jpa-patterns

JPA/Hibernate Patterns

Use for data modeling, repositories, and performance tuning in Spring Boot.

When to Activate

• Designing JPA entities and table mappings
• Defining relationships (@OneToMany, @ManyToOne, @ManyToMany)
• Optimizing queries (N+1 prevention, fetch strategies, projections)
• Configuring transactions, auditing, or soft deletes
• Setting up pagination, sorting, or custom repository methods
• Tuning connection pooling (HikariCP) or second-level caching

Entity Design

@Entity
@Table(name = "markets", indexes = {
  @Index(name = "idx_markets_slug", columnList = "slug", unique = true)
})
@EntityListeners(AuditingEntityListener.class)
public class MarketEntity {
  @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @Column(nullable = false, length = 200)
  private String name;

  @Column(nullable = false, unique = true, length = 120)
  private String slug;

  @Enumerated(EnumType.STRING)
  private MarketStatus status = MarketStatus.ACTIVE;

  @CreatedDate private Instant createdAt;
  @LastModifiedDate private Instant updatedAt;
}

Enable auditing:

@Configuration
@EnableJpaAuditing
class JpaConfig {}

Relationships and N+1 Prevention

@OneToMany(mappedBy = "market", cascade = CascadeType.ALL, orphanRemoval = true)
private List<PositionEntity> positions = new ArrayList<>();

• Default to lazy loading; use JOIN FETCH in queries when needed
• Avoid EAGER on collections; use DTO projections for read paths

@Query("select distinct m from MarketEntity m left join fetch m.positions where m.id = :id")
Optional<MarketEntity> findWithPositions(@Param("id") Long id);

Note: DISTINCT is required when fetch-joining a one-to-many collection — without it, the root entity is duplicated once per child row in the result set. For single-result queries (findById) the duplication is harmless, but for list queries it produces duplicate root objects. Hibernate 6+ applies de-duplication automatically in some cases, but explicit DISTINCT keeps behavior portable and clear.