Question

在我的Java项目中，我具有这三个类和一个用于插入数据的代码：

@Entity(name = "Quiz")
@Table(name = "quiz")
public class Quiz implements Serializable {
    private static final long serialVersionUID = 1L;

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

    private String name;

    @ManyToOne(cascade= CascadeType.ALL)
    private Skill skill;

    @ManyToMany(fetch = FetchType.EAGER, cascade=CascadeType.ALL)
    private List<StudentClass> stClasses= new ArrayList<>();


@Entity
public class Skill implements Serializable {
    private static final long serialVersionUID = 1L;

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


@Entity
@Table(name = "Student_Class")
@PrimaryKeyJoinColumn(name="id")
public class StudentClass implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String name;

    @OneToMany(fetch= FetchType.EAGER, cascade = { CascadeType.ALL })
    @JoinColumn(name = "stClass_id", referencedColumnName="id")
    private Set<User> students=new HashSet<>();

    @ManyToMany(fetch= FetchType.EAGER, mappedBy="stClasses", cascade=CascadeType.ALL)
    private Set<Quiz> quizzes= new HashSet<>();

@Transactional
public void save(Quiz quiz) {
    hibernateTemplate.saveOrUpdate(quiz);
}

但是如果我插入一个已经使用了Skill的StudentClass的测验，则会出现此错误：

GRAVE: Servlet.service() for servlet [appServlet] in context with path [/AutoQuiz3000] threw exception [Request processing failed; nested exception is org.springframework.dao.DuplicateKeyException: A different object with the same identifier value was already associated with the session : [fr.dawan.autoquiz3000.beans.Skill#10]; nested exception is org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already associated with the session : [fr.dawan.autoquiz3000.beans.Skill#10]] with root cause
org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already associated with the session : [fr.dawan.autoquiz3000.beans.Skill#10]
at org.hibernate.engine.internal.StatefulPersistenceContext.checkUniqueness(StatefulPersistenceContext.java:648)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.performUpdate(DefaultSaveOrUpdateEventListener.java:284)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsDetached(DefaultSaveOrUpdateEventListener.java:227)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:92)

示例：

quiz.setName("what the capital...");
quiz.setSkill("geography");
quiz.addstClass("formation Java");

quiz.setName("what the money...");
quiz.setSkill("geography");
quiz.addstClass("formation Java");

我有一个错误，因为StudentClass已经在使用Skill！如果我更改了StudentClass，我没问题。

不知道问题出在哪里！有人有主意吗？

非常感谢您！

Answer 1

您的问题是，由于使用了Cascade.ALL注释，当您尝试使用saveAndUpdate或persist时，这命令Hibernate尝试插入一个新实体，在您的情况下，该实体已经存在。因此，您无需合并其中的一种方法，而需要合并您的实体，该实体将首先检查是否存在，然后尝试插入，否则将简单地进行更新。

因此，您需要进行以下更改。

@Entity(name = "Quiz")
@Table(name = "quiz")
public class Quiz implements Serializable {
    private static final long serialVersionUID = 1L;

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

    private String name;

    @ManyToOne(cascade= CascadeType.MERGE)
    private Skill skill;

    @ManyToMany(fetch = FetchType.EAGER, cascade=CascadeType.ALL)
    private List<StudentClass> stClasses= new ArrayList<>();
}

在存储库中，您将需要使用merge(entity)。希望这会有所帮助！

具有相同标识符值的另一个对象已被关联

1 个答案: