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@EnableJpaAuditingclass 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.

Repository Patterns

public interface MarketRepository extends JpaRepository<MarketEntity, Long> {  Optional<MarketEntity> findBySlug(String slug);
  @Query("select m from MarketEntity m where m.status = :status")  Page<MarketEntity> findByStatus(@Param("status") MarketStatus status, Pageable pageable);}

• Use projections for lightweight queries:

public interface MarketSummary {  Long getId();  String getName();  MarketStatus getStatus();}Page<MarketSummary> findAllBy(Pageable pageable);

Transactions

• Annotate service methods with @Transactional
• Use @Transactional(readOnly = true) for read paths to optimize
• Choose propagation carefully; avoid long-running transactions

@Transactionalpublic Market updateStatus(Long id, MarketStatus status) {  MarketEntity entity = repo.findById(id)      .orElseThrow(() -> new EntityNotFoundException("Market"));  entity.setStatus(status);  return Market.from(entity);}

Pagination

PageRequest page = PageRequest.of(pageNumber, pageSize, Sort.by("createdAt").descending());Page<MarketEntity> markets = repo.findByStatus(MarketStatus.ACTIVE, page);

For cursor-like pagination, include id > :lastId in JPQL with ordering.

Indexing and Performance

• Add indexes for common filters (status, slug, foreign keys)
• Use composite indexes matching query patterns (status, created_at)
• Avoid select *; project only needed columns
• Batch writes with saveAll and hibernate.jdbc.batch_size

Connection Pooling (HikariCP)

Recommended properties:

spring.datasource.hikari.maximum-pool-size=20spring.datasource.hikari.minimum-idle=5spring.datasource.hikari.connection-timeout=30000spring.datasource.hikari.validation-timeout=5000

For PostgreSQL LOB handling, add:

spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation=true

Caching

• 1st-level cache is per EntityManager; avoid keeping entities across transactions
• For read-heavy entities, consider second-level cache cautiously; validate eviction strategy

Migrations

• Use Flyway or Liquibase; never rely on Hibernate auto DDL in production
• Keep migrations idempotent and additive; avoid dropping columns without plan

Testing Data Access

• Prefer @DataJpaTest with Testcontainers to mirror production
• Assert SQL efficiency using logs: set logging.level.org.hibernate.SQL=DEBUG and logging.level.org.hibernate.orm.jdbc.bind=TRACE for parameter values

Remember: Keep entities lean, queries intentional, and transactions short. Prevent N+1 with fetch strategies and projections, and index for your read/write paths.