Java JPA Hibernate Skill

Master data persistence with JPA and Hibernate for production applications.

Overview

This skill covers JPA entity design, Hibernate optimization, Spring Data repositories, query strategies, and caching. Focuses on preventing N+1 queries and building high-performance persistence layers.

When to Use This Skill

Use when you need to:

Design JPA entities with relationships Optimize database queries Configure Hibernate for performance Implement caching strategies Debug persistence issues Topics Covered Entity Design Entity mapping annotations Relationship types (1:1, 1:N, N:M) Inheritance strategies Lifecycle callbacks Auditing Query Optimization N+1 problem prevention JOIN FETCH vs EntityGraph Batch fetching Projections and DTOs Transactions @Transactional configuration Propagation and isolation Optimistic vs pessimistic locking Deadlock prevention Caching First and second level cache Query cache Cache invalidation Redis integration Quick Reference // Entity with relationships @Entity @Table(name = "orders") public class Order {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "customer_id", nullable = false)
private Customer customer;

@OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
@BatchSize(size = 20)
private List<OrderItem> items = new ArrayList<>();

@Version
private Long version;

// Bidirectional helper
public void addItem(OrderItem item) {
    items.add(item);
    item.setOrder(this);
}

}

// Auditing base class @MappedSuperclass @EntityListeners(AuditingEntityListener.class) public abstract class Auditable { @CreatedDate @Column(updatable = false) private Instant createdAt;

@LastModifiedDate
private Instant updatedAt;

}

// Repository with query optimization public interface OrderRepository extends JpaRepository {

// JOIN FETCH to prevent N+1
@Query("SELECT DISTINCT o FROM Order o JOIN FETCH o.items WHERE o.status = :status")
List<Order> findByStatusWithItems(@Param("status") Status status);

// EntityGraph alternative
@EntityGraph(attributePaths = {"items", "customer"})
Optional<Order> findById(Long id);

// DTO Projection
@Query("SELECT new com.example.OrderSummary(o.id, o.status, c.name) " +
       "FROM Order o JOIN o.customer c WHERE o.id = :id")
Optional<OrderSummary> findSummaryById(@Param("id") Long id);

}

N+1 Prevention Strategies Strategy Use When Example JOIN FETCH Always need relation JOIN FETCH o.items EntityGraph Dynamic fetching @EntityGraph(attributePaths) @BatchSize Collection access @BatchSize(size = 20) DTO Projection Read-only queries new OrderSummary(...) Hibernate Configuration spring: jpa: open-in-view: false # Critical! properties: hibernate: jdbc.batch_size: 50 order_inserts: true order_updates: true default_batch_fetch_size: 20 generate_statistics: ${HIBERNATE_STATS:false}

datasource: hikari: maximum-pool-size: 20 minimum-idle: 5 leak-detection-threshold: 60000

Troubleshooting Common Issues Problem Cause Solution N+1 queries Lazy in loop JOIN FETCH, EntityGraph LazyInitException Session closed DTO projection Slow queries Missing index EXPLAIN ANALYZE Connection leak No @Transactional Add annotation Debug Properties spring.jpa.show-sql=true logging.level.org.hibernate.SQL=DEBUG logging.level.org.hibernate.orm.jdbc.bind=TRACE hibernate.generate_statistics=true

Debug Checklist □ Enable SQL logging □ Check query count per request □ Verify fetch strategies □ Review @Transactional □ Check connection pool

Usage Skill("java-jpa-hibernate")

Related Skills java-performance - Query optimization java-spring-boot - Spring Data

安装