java - Controller 和 hibernate 集成。未保存实体

Question

我对 Hibernate 提供的 JPA 有问题。这是我的实体:

@Entity
public class Action {
    @Id
    @GeneratedValue
    private Integer id;

    @Column
    private String name;

    @JoinColumn
    @ManyToOne
    private User user;

    public Integer getId() { return this.id; }
    protected void setId(Integer id) { this.id = id; }

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

    public void getUser() { return this.user; }
    protected void setUser(User user) { this.user = user; }
}
@Entity
public class User {
    @Id
    @GeneratedValue
    private Integer id;

    @Column
    private String name;

    @OneTomany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    private List<Action> actions = new ArrayList<>();

    public Integer getId() { return this.id; }
    protected void setId(Integer id) { this.id = id; }

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

    public void addAction(Action action) {
        action.setUser(this);
        actions.add(action);
    }
    public void removeAction(Action action) {
        actions.remove(action);
        action.setUser(null);
    }
    public List<Action> getActions() { return Collections.unmodifiableList(actions); }
}

这是我的 Controller 代码:

@Controller
@RequestMapping("/user/{username}")
@SessionAttributes("user")
public class ActionController {
    @Autowired
    private TestService service;

    @ModelAttribute("user")
    public User contextRegistration(@PathVariable("username") String username) {
        return this.service.getByName(username);
    }

    @RequestMapping("")
    public String userView() {
        return "user";
    }

    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public String addAction(@ModelAttribute Action action) {
        return "addAction";
    }

    @RequestMapping(value = "/add", method = RequestMethod.POST)
    public String postAddAction(@Valid Action action, BindingResult result, User user, SessionStatus sessionStatus) {
        if(result.hasErrors()) {
            return "addAction";
        }

        user.addAction(action);
        this.service.saveAction(action);
        sessionStatus.setComplete();
        return "redirect:/user/{username}";
    }
}

当执行 postAddAction 方法时，出现以下错误:

org.hibernate.TransientPropertyValueException: object references an unsaved transient instance - save the transient instance before flushing : pl.zaprogramowany.test.model.Action.user -> pl.zaprogramowany.test.model.User

在执行方法 saveAction 的行中。

我的代码是以此代码为蓝本的 https://github.com/spring-projects/spring-petclinic/blob/master/src/main/java/org/springframework/samples/petclinic/web/PetController.java#L79但我不知道为什么会出现此错误，因为我的代码与此非常相似。

有人可以帮忙吗？

@编辑

我正在使用 spring Jpa 存储库，服务层中的代码非常简单。

@Transactional(readyOnly = true)
public User getByName(String name) {
    return this.userRepository.getByName(name);
}

@Transactional
public void saveAction(Action action) {
    this.actionRepository.save(action);
}

Answer 1

当您的集合映射中未包含 cascade="all"(如果使用 xml)或 cascade=CascadeType.ALL(如果使用注释)时，就会出现此问题。

在您的情况下存在，但在用户实体而不是在操作实体

因此我们需要了解如何保存操作实体，在此基础上我们可以决定是否需要在操作实体上添加级联