Spring Data Jpa

Spring Data JPA

Overview

Provides patterns for Spring Data JPA repositories, entity relationships, queries, pagination, auditing, and transactions.

When to Use

Creating repositories with CRUD operations, entity relationships, @Query annotations, pagination, auditing, or UUID primary keys.

Instructions

Create Repository Interfaces

To implement a repository interface:

• Extend the appropriate repository interface:

   @Repository
   public interface UserRepository extends JpaRepository<User, Long> {
       // Custom methods defined here
   }

• Use derived queries for simple conditions:

   Optional<User> findByEmail(String email);
   List<User> findByStatusOrderByCreatedDateDesc(String status);

• Implement custom queries with @Query:

   @Query("SELECT u FROM User u WHERE u.status = :status")
   List<User> findActiveUsers(@Param("status") String status);

Configure Entities

• Define entities with proper annotations:

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

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

• Configure relationships using appropriate cascade types:

   @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, orphanRemoval = true)
   private List<Order> orders = new ArrayList<>();

Validation: Test cascade behavior with a small dataset before applying to production data. Verify delete operations don't cascade unexpectedly.

• Set up database auditing:

   @CreatedDate
   @Column(nullable = false, updatable = false)
   private LocalDateTime createdDate;

Apply Query Patterns

• Use derived queries for simple conditions
• Use @Query for complex queries
• Return Optional<T> for single results
• Use Pageable for pagination
• Apply @Modifying for update/delete operations

Manage Transactions

• Mark read-only operations with @Transactional(readOnly = true)
• Use explicit transaction boundaries for modifying operations
• Specify rollback conditions when needed

Validate and Optimize

1. Verify entity configuration:

• Test cascade behavior in a transaction before production deployment
• Validate bidirectional relationships sync correctly

2. Optimize query performance:

• Run EXPLAIN ANALYZE on queries against large tables
• If performance issues detected: add indexes → verify with EXPLAIN → repeat
• Use @EntityGraph to prevent N+1 queries

3. Validate pagination:

• Ensure indexed columns support pagination queries
• Test with large datasets to verify cursor stability

Examples

Basic CRUD Repository

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {
    // Derived query
    List<Product> findByCategory(String category);

    // Custom query
    @Query("SELECT p FROM Product p WHERE p.price > :minPrice")
    List<Product> findExpensiveProducts(@Param("minPrice") BigDecimal minPrice);
}

Pagination Implementation

@Service
public class ProductService {
    private final ProductRepository repository;

    public Page<Product> getProducts(int page, int size) {
        Pageable pageable = PageRequest.of(page, size, Sort.by("name").ascending());
        return repository.findAll(pageable);
    }
}

Entity with Auditing

@Entity
@EntityListeners(AuditingEntityListener.class)
public class Order {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @CreatedDate
    @Column(nullable = false, updatable = false)
    private LocalDateTime createdDate;

    @LastModifiedDate
    private LocalDateTime lastModifiedDate;

    @CreatedBy
    @Column(nullable = false, updatable = false)
    private String createdBy;
}

Best Practices

Entity Design

• Use constructor injection exclusively (never field injection)
• Prefer immutable fields with final modifiers
• Use Java records (16+) or @Value for DTOs
• Always provide proper @Id and @GeneratedValue annotations
• Use explicit @Table and @Column annotations

Performance Optimization

• Use appropriate fetch strategies (LAZY vs EAGER)
• Implement pagination for large datasets
• Use database indexes for frequently queried fields
• Consider using @EntityGraph to avoid N+1 query problems

Reference Documentation

For comprehensive examples, detailed patterns, and advanced configurations, see:

• Examples - Complete code examples for common scenarios
• Reference - Detailed patterns and advanced configurations

Constraints and Warnings

• Never expose JPA entities directly in REST APIs; always use DTOs to prevent lazy loading issues.
• Avoid N+1 query problems by using @EntityGraph or JOIN FETCH in queries.
• Be cautious with CascadeType.REMOVE on large collections as it can cause performance issues.
• Do not use EAGER fetch type for collections; it can cause excessive database queries.
• Avoid long-running transactions as they can cause database lock contention.
• Use @Transactional(readOnly = true) for read operations to enable optimizations.
• Be aware of the first-level cache; entities may not reflect database changes within the same transaction.
• UUID primary keys can cause index fragmentation; consider using sequential UUIDs or Long IDs.
• Pagination on large datasets requires proper indexing to avoid full table scans.