SpringBoot4整合Spring Data JPA的实战教程

<dependencies>
    <!-- JPA Starter -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <!-- MySQL 驱动 -->
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <scope>runtime</scope>
    </dependency>
    <!-- Druid（可选） -->
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>druid-spring-boot-3-starter</artifactId>
        <version>1.2.23</version>
    </dependency>
</dependencies>

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/jpa_demo?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai&useSSL=false
    username: root
    password: root
    driver-class-name: com.mysql.cj.jdbc.Driver
  jpa:
    show-sql: true
    hibernate:
      ddl-auto: update
    properties:
      hibernate:
        format_sql: true
        dialect: org.hibernate.dialect.MySQLDialect

@Entity
@Table(name = "t_user")
public class User {

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

    @Column(name = "username", nullable = false, length = 50)
    private String username;

    @Column(name = "email", length = 100)
    private String email;

    @Column(name = "age")
    private Integer age;

    @Column(name = "create_time")
    private LocalDateTime createTime;

    // 必须有无参构造器
    public User() {}

    // getter / setter
}

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

@Id
@GeneratedValue(strategy = GenerationType.UUID)      // UUID
private String id;

public interface UserRepository extends JpaRepository<User, Long> {
}

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public User create(User user) {
        user.setCreateTime(LocalDateTime.now());
        return userRepository.save(user);
    }

    public User getById(Long id) {
        return userRepository.findById(id)
                .orElseThrow(() -> new BusinessException(ResultCode.NOT_FOUND, "用户不存在"));
    }

    public List<User> listAll() {
        return userRepository.findAll();
    }

    public void delete(Long id) {
        userRepository.deleteById(id);
    }
}

public interface UserRepository extends JpaRepository<User, Long> {

    // WHERE username = ?
    User findByUsername(String username);

    // WHERE email LIKE %?
    List<User> findByEmailContaining(String email);

    // WHERE age >= ? AND username = ?
    List<User> findByAgeGreaterThanEqualAndUsername(int age, String username);

    // WHERE create_time BETWEEN ? AND ?
    List<User> findByCreateTimeBetween(LocalDateTime start, LocalDateTime end);

    // ORDER BY create_time DESC
    List<User> findByOrderByCreateTimeDesc();

    // 分页 + 排序
    Page<User> findByAge(int age, Pageable pageable);
}

// 分页
Pageable pageable = PageRequest.of(0, 10, Sort.by("createTime").descending());
Page<User> page = userRepository.findByAge(18, pageable);

// 结果
page.getContent();   // 数据列表
page.getTotalPages(); // 总页数
page.getTotalElements(); // 总记录数
page.getNumber();    // 当前页码

@Entity
@Table(name = "t_order")
public class Order {

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

    private String orderNo;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private User user;
}

@Entity
@Table(name = "t_user")
public class User {

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

    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private List<Order> orders = new ArrayList<>();
}

@Configuration
@EnableJpaAuditing
public class JpaConfig {
}

@Entity
@Table(name = "t_user")
@EntityListeners(AuditingEntityListener.class)
public class User {

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

    @CreatedDate
    @Column(name = "create_time")
    private LocalDateTime createTime;

    @LastModifiedDate
    @Column(name = "update_time")
    private LocalDateTime updateTime;

    @CreatedBy
    @Column(name = "created_by")
    private String createdBy;

    @LastModifiedBy
    @Column(name = "updated_by")
    private String updatedBy;
}