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<Order, Long> {

    // 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