是否可以创建具有两个主键值的实体？

Question

我有一个问题，一个Entity包含一个unique_key所以我可能需要的是创建Entity与两个PrimaryKey甚至可能吗？

这是我的Entity

@Entity
public class UserAnswerQuestion extends DateAudit {

    @Id
    @Column(name = "useranswerquestion_id")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "useranswerquestion_seq")
    @SequenceGenerator(name = "useranswerquestion_seq", allocationSize = 1)
    private Long id;

    @ManyToOne
    private User user;
    @ElementCollection
    private List<Answer> answerList;
    @ManyToOne
    private Question question;

    private Boolean passed;

    private Boolean shown;

    public UserAnswerQuestion(){
    }
....

当我尝试用另一个Entity创建这个User的问题时，它说：

org.postgresql.util.PSQLException：错误：重复键值违反唯一约束“uk_6v3tlg1gflua8r8d4wlqxo7v5”详细信息：键（answer_list_answer_id）=（11）已存在。

所以我想做的就是尽可能将User作为@Id，也许它解决了我的问题......

编辑

我做的是，像这样创建一个类UserAnswerQuestionId：

public class UserAnswerQuestionId implements Serializable {

@Column(name = "useranswerquestion_id")
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "useranswerquestion_seq")
@SequenceGenerator(name = "useranswerquestion_seq", allocationSize = 1)
private Long id;

@Column(name ="user_id")
private Long user_id;

public UserAnswerQuestionId(){

}

public UserAnswerQuestionId(Long user_id) {
    this.user_id = user_id;
}

然后在UserAnswerQuestion实体中我将其更改为：

 @EmbeddedId
 private UserAnswerQuestionId userAnswerQuestionId;

但错误现在说：

org.hibernate.id.IdentifierGenerationException: null id generated for:class com.pew.model.useranswers.UserAnswerQuestion
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:192) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:135) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:62) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:800) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:785) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]

编辑2

我正在仔细阅读错误，看起来问题就在于

@ElementCollection
private List<Answer> answerList;

我如何解决这个问题，以便在这个Entity上重复这个元素？

也许我可以定义那些@ElementCollection不是唯一的？那么可以在这个实体上重复一次吗？

这是我的Answer实体

@Entity(name = "answer")
public class Answer extends DateAudit {

@Id
@Column(name = "answer_id")
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "answer_seq")
@SequenceGenerator(name = "answer_seq", allocationSize = 1)
private Long id;

@Column(name = "answerToQuestion")
private String answerToQuestion;

Answer 1

也许您可能需要更好地解释您的用例。从上下文信息看起来，您想要检索用户和他们为各种问题提供的答案。在这种情况下，您可能只需要一个如下所示的关联表。

public class User extends DateAudit { //This assumes you are intested in retrieving User and their answer(s) in the domain model.

    @Id
    private Long id; //userid.



    @ManyToMany
    @JoinTable(name = “ANSWERS_FOR_QUESTIONS”, //More appropriate name may be : ANSWERS_BY_USERS
           joinColumns = { @JoinColumn(name = “user_id”) }, //fk
           inverseJoinColumns = { @JoinColumn(name = “question_id”) }) //fk
    private Set<Answers> answers = new HashSet<Answers>();

Answer 2

主键始终只有1且唯一。它可以是由多列元组组成的复合键。

Answer 3

使用UserAnswerQuestionId包括你的@IdClass应该工作：

@Entity
@IdClass(UserAnswerQuestionId.class)
public class UserAnswerQuestion extends DateAudit {

    @Id
    private Long id;

    @Id
    private Long user_id;

    @ElementCollection
    private List<Answer> answerList;
    @ManyToOne
    private Question question;

    private Boolean passed;

    private Boolean shown;

    public UserAnswerQuestion(){
    }