Question

我在Spring Boot上有以下Web应用程序。在控制器层，我可以通过JpaRepository（getOne方法）和Hibernate会话（getUserByKey方法）以两种方式获取用户控制器层：

@RestController
@RequestMapping("desk")
public class MainController {

    final UserService userService;

    @Autowired
    public MainController(UserService userService) {
        this.userService = userService;
    }

    @GetMapping("{id}")
    public User getUser(@PathVariable long id) {
       // User user = userService.getOne(id);     //through the JpaRepository
       User user = userService.getUserByKey(id);  //through the hibernate session 
       return user;
    }
}

我的数据库中有一个拥有两辆车的用户（一对多）

层模型：

用户表：

@Entity
@Table(name = "user")
@ToString(of = {"id", "test"})
@EqualsAndHashCode(of = {"id"})
public class User {
    public User() {
    }

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

    private String name;

    private String address;

    @OneToMany(cascade = {CascadeType.ALL}, fetch = FetchType.LAZY, targetEntity = Car.class)
    @JoinTable(name = "car", joinColumns = @JoinColumn(name = "ownerId", referencedColumnName = "id"))
    private List<Car> childIds;

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public List<Car> getChildIds() {
        return childIds;
    }

    public void setChildIds(List<Car> childIds) {
        this.childIds = childIds;
    }
}

汽车桌：

@Entity
@Table(name = "car")
@ToString(of = {"id", "test"})
@EqualsAndHashCode(of = {"id"})
public class Car {
    public Car() {
    }

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

    private long ownerId;

    private String model;

    @ManyToOne(cascade = {CascadeType.ALL}, fetch = FetchType.LAZY, targetEntity = User.class)
    @JoinTable(name = "user", joinColumns = @JoinColumn(name = "id", referencedColumnName = "id"))
    private List<Long> parentIds;

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public long getOwnerId() {
        return ownerId;
    }

    public void setOwnerId(long ownerId) {
        this.ownerId = ownerId;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public List<Long> getParentIds() {
        return parentIds;
    }

    public void setParentIds(List<Long> parentIds) {
        this.parentIds = parentIds;
    }
}

服务层：

@Service
@Transactional
public class UserServiceImple implements UserService {

    final UserRepo userRepo;
    final DAO userDAO;

    @Autowired
    public UserServiceImple(UserRepo userRepo, DAO userDAO) {
        this.userRepo = userRepo;
        this.userDAO = userDAO;
    }

    public User getOne(long id) {
        return userRepo.getOne(id); //through the JpaRepository
    }

    @Override
    public User getUserByKey(long id) {
        return userDAO.getUserFromBd(id); //through the hibernate session 
    }
}

JPA存储库：

@Repository
public interface UserRepo extends JpaRepository<User, Long> {

}

DAO层：

@Repository
public class DAO implements GenericDao<User> {

    private SessionFactory hibernateFactory;

    @Autowired
    public DAO(EntityManagerFactory factory) {
        if (factory.unwrap(SessionFactory.class) == null) {
            throw new NullPointerException("factory is not a hibernate factory");
        }
        this.hibernateFactory = factory.unwrap(SessionFactory.class);
    }

    @Override
    public User getUserFromBd(long user_id) {

        Object query = hibernateFactory.openSession().createQuery("FROM User WHERE id =:user_id")
                .setParameter("user_id", user_id)
                .uniqueResult();
        return (User) query;
    }
}

问题：

1）为什么当我使用hibernet会话（getUserByKey方法）获取用户时，即使所有模型上的fetch = FetchType.LAZY都在控制器的调试中看到一个对象？

2）为什么当我使用JpaRepository（getOne方法）获取用户时，即使在所有模型上fetch = FetchType.EAGER，在控制器中的调试中我都可以看到一个代理对象？

3）如何使用JpaRepository获取对象？

4）如何使用hibernet会话将获取类型（EAGER）切换为FetchType.LAZY？

为什么用户通过hibernet会话并通过JpaRepository作为代理对象从数据库作为对象返回？

0 个答案: