JPA

JPA Annotations

@Entity
@Table(name = "products")
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, length = 100)
    private String name;

    @ManyToOne
    @JoinColumn(name = "category_id")
    private Category category;

    @OneToMany(mappedBy = "product", cascade = CascadeType.ALL)
    private List<Review> reviews;
}

JPA vs Hibernate

Aspect	JPA	Hibernate
Type	Specification	Implementation
Annotations	Standard	Standard + proprietary

Entity Design

• Use @Column for constraints
• Implement equals/hashCode properly
• Use @Version for optimistic locking
• Map relationships correctly

Query Optimization

• Use JPQL over Criteria
• Implement pagination
• Use @Query for complex queries
• Avoid N+1 problems

Performance

• Use batch fetching
• Implement second-level cache
• Use read-only transactions
• Optimize lazy loading

Key Points

• Understanding JPA is essential for production systems
• Always consider scalability and maintainability
• Test thoroughly before deploying to production
• Monitor performance and set up alerting

Common Patterns

1. Validation: Always validate input at the boundary
2. Error Handling: Use structured error responses
3. Logging: Log key events for debugging
4. Testing: Unit, integration, and load tests
5. Documentation: Keep docs updated with code changes