spring-data-jpa

Spring Data JPA

Overview

To implement persistence layers with Spring Data JPA, create repository interfaces that provide automatic CRUD operations, entity relationships, query methods, and advanced features like pagination, auditing, and performance optimization.

When to Use

Use this Skill when:

• Implementing repository interfaces with automatic CRUD operations

• Creating entities with relationships (one-to-one, one-to-many, many-to-many)

• Writing queries using derived method names or custom @Query annotations

• Setting up pagination and sorting for large datasets

• Implementing database auditing with timestamps and user tracking

• Configuring transactions and exception handling

• Using UUID as primary keys for distributed systems

• Optimizing performance with database indexes

• Setting up multiple database configurations

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<>();

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 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

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

Repository Queries

• Use derived queries for simple conditions

• Use @Query for complex queries to avoid long method names

• Always use @Param for query parameters

• Return Optional<T> for single results

• Apply @Transactional on modifying operations

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

Transaction Management

• Mark read-only operations with @Transactional(readOnly = true)

• Use explicit transaction boundaries

• Avoid long-running transactions

• Specify rollback conditions when needed

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.

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