JPA，Hibernate:具有关联的复合密钥.为什么加载而不保存

Question

我正在尝试映射3个实体：Question、Answer和QuestionDisplayRule。问题有许多答案和许多问题显示规则，每个规则都属于一个问题。QuestionDisplayRule有一个Question、一个Answer和一个String值字段。QuestionDisplayRule的数据库表如下所示：

create table question_display_rule(
    question_id int, 
    answer_id int, 
    answer_value varchar(128)
);

当然，question_id和answer_id是PK。

JPA映射如下：

@Embeddable
public class QuestionDisplayRulePK implements Serializable {
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name="question_id", insertable = false, updatable = false)
    private Question question;
    @ManyToOne
    @JoinColumn(name = "answer_id", insertable = false, updatable = false)
    private Answer answer;
}

和

@Entity
@Table(name = "question_display_rule")
public class QuestionDisplayRule implements Serializable {
    @EmbeddedId
    private QuestionDisplayRulePK id;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name="question_id", insertable = false, updatable = false)
    private Question question;
    @ManyToOne
    @JoinColumn(name = "answer_id", insertable = false, updatable = false)
    private Answer answer;
    @Column(name="answer_value")
    private String answerValue;
}

问题是，如果我在DB中手动添加记录，但不保存它们，那么它加载QuestionDisplayRules就很好。没有错误，什么都没有。。

测试代码：

    QuestionDisplayRulePK qPK = new QuestionDisplayRulePK();
    qPK.setQuestion(q);
    qPK.setAnswer(a);
    QuestionDisplayRule qr = new QuestionDisplayRule(qPK, "Yes");
    qr.setAnswerValue("whateva..");
    ....
    // DAO code looks like: getSession().saveOrUpdate(qr);

有什么想法吗？谢谢

Answer 1

您正在将实体映射到可嵌入对象中，这是错误的。可嵌入的应该只包含基类型。简而言之，你的实体应该是这样的：

@Entity
public class Question
{
    @Id
    @GeneratedValue
    @Column(name = "id")
    private Long id;
    @OneToMany(mappedBy = "question")
    private Set<Answer> answers;
}
@Entity
public class Answer
{
    @Id
    @GeneratedValue
    @Column(name = "id")
    private Long id;
    @ManyToOne
    private Question question;
}
@Entity
public class QuestionDisplayRule
{
    @EmbeddedId
    private QuestionDisplayRulePK key;
    @MapsId(value = "questionId")
    @ManyToOne
    @JoinColumn(name = "question_id", referencedColumnName = "id")
    private Question question;
    @MapsId(value = "answerId")
    @ManyToOne
    @JoinColumn(name = "answer_id", referencedColumnName = "id")
    private Answer answer;
}
@Embeddable
public class QuestionDisplayRulePK
{
    @Column(name = "answer_id")
    private Long answerId;
    @Column(name = "question_id")
    private Long questionId;
}