Spring Data JPA 语法详解与使用案例详解

public interface UserRepository extends JpaRepository<User, Long> {
// 自动实现的查询方法
}

User save(User user);// 保存
Optional<User> findById(Long id);// 查询
List<User> findAll();// 查询所有
long count();// 计数
void deleteById(Long id);// 删除

public interface UserRepository extends JpaRepository<User, Long> {
List<User> findByUsername(String username);// SELECT * FROM user WHERE username = ?
}

List<User> findByUsernameAndEmail(String username, String email);// AND 条件
List<User> findByUsernameOrEmail(String username, String email);// OR 条件

List<User> findByUsernameOrderByEmailAsc(String username);// 升序
List<User> findByUsernameOrderByEmailDesc(String username); // 降序

Page<User> findByUsername(String username, Pageable pageable);// 分页查询

@Query("SELECT u FROM User u WHERE u.username LIKE %:keyword%")
List<User> searchByUsername(@Param("keyword") String keyword);

@Query(value = "SELECT * FROM user WHERE email = ?1",
nativeQuery = true)
User findByEmailNative(String email);

public interface UserRepository extends JpaRepository<User, Long> {
Page<User> findAll(Pageable pageable);
}

Pageable pageable = PageRequest.of(0, 10, Sort.by("id").descending());
Page<User> users = userRepository.findAll(pageable);

public class UserSpecifications {
public static Specification<User> hasUsername(String username) {
return (root, query, cb) -> cb.equal(root.get("username"), username);
}
}

public interface UserRepository extends JpaRepository<User, Long>, JpaSpecificationExecutor<User> {
// 动态查询
}
// 调用示例
List<User> users = userRepository.findAll(UserSpecifications.hasUsername("admin"));

@Entity
public class User {
@Id
private Long id;
@OneToOne
@JoinColumn(name = "profile_id")
private Profile profile;
}

@Entity
public class User {
@Id
private Long id;
@OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
private List<Order> orders;
}

@Entity
public class User {
@Id
private Long id;
@ManyToMany
@JoinTable(
name = "user_role",
joinColumns = @JoinColumn(name = "user_id"),
inverseJoinColumns = @JoinColumn(name = "role_id")
)
private Set<Role> roles;
}

@Service
public class UserService {
@Autowired
private UserRepository userRepository;
@Transactional
public void transferMoney(Long fromId, Long toId, Double amount) {
User fromUser = userRepository.findById(fromId).orElseThrow(...);
User toUser = userRepository.findById(toId).orElseThrow(...);
fromUser.setBalance(fromUser.getBalance() - amount);
toUser.setBalance(toUser.getBalance() + amount);
userRepository.save(fromUser);
userRepository.save(toUser);
}
}

// 使用 JOIN FETCH 一次性加载关联数据
@Query("SELECT u FROM User u JOIN FETCH u.orders WHERE u.id = :id")
User findUserWithOrders(@Param("id") Long id);

spring:
jpa:
open-in-view: false
cache:
type: caffeine

@Entity
public class User {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String username;
private String email;
@OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
private List<Order> orders = new ArrayList<>();
}

public interface UserRepository extends JpaRepository<User, Long> {
List<User> findByUsername(String username);
Page<User> findAll(Pageable pageable);
}

@Service
public class UserService {
@Autowired
private UserRepository userRepository;
public User createUser(String username, String email) {
User user = new User();
user.setUsername(username);
user.setEmail(email);
return userRepository.save(user);
}
public Page<User> searchUsers(int page, int size) {
Pageable pageable = PageRequest.of(page, size);
return userRepository.findAll(pageable);
}
}

@RestController
@RequestMapping("/users")
public class UserController {
@Autowired
private UserService userService;
@PostMapping
public User createUser(@RequestBody UserDTO dto) {
return userService.createUser(dto.getUsername(), dto.getEmail());
}
@GetMapping
public Page<User> getUsers(@RequestParam int page, @RequestParam int size) {
return userService.searchUsers(page, size);
}
}