级联保存具有外键的实体对象作为复合主键的一部分

Question

我想将我的 QuestionCompletion 类的对象与所有子元素一起保留。其中一个孩子有一个复合主键。作为这个主键的一部分，我还有另一个实体的外键。结果我收到了这个错误：

Exception caught during request processing: javax.ejb.EJBTransactionRolledbackException:
could not set a field value by reflection setter of com.example.model.domain.QuestionCompletionAnswerPK.questionCompletionId
javax.ejb.EJBTransactionRolledbackException: could not set a field value by reflection
setter of com.example.model.domain.QuestionCompletionAnswerPK.questionCompletionId

而最后一个“由”当然是NullPointerException：

Caused by: java.lang.NullPointerException

这是我的代码的一部分。最后一行导致错误。

QuestionCompletion questionCompletion = new QuestionCompletion();
List<QuestionCompletionAnswer> answers = new ArrayList<QuestionCompletionAnswer>();
for (;;) { // loop isn't important; it's loop for answers
    ExtendedQuestion extendedQuestion = new ExtendedQuestion();
    extendedQuestion.setId(extendedQuestionId); //extendedQuestionId is known to me in that place
    for (;;) { // loop isn't important; it's loop for question answers
        //questionCompletion and extendedQuestion are popualted here
        QuestionCompletionAnswer questionCompletionAnswer = new QuestionCompletionAnswer();
        questionCompletionAnswer.setQuestionCompletion(questionCompletion); 
        questionCompletionAnswer.setExtendedQuestion(extendedQuestion); 
        answers.add(questionCompletionAnswer);
    }
}
questionCompletion.setAnswers(answers);
questionCompletionService.saveOrMerge(questionCompletion);

这是我希望保留其所有子元素的基本实体类。我意识到List<QuestionCompletionAnswer> 会导致问题。我已经使用cascade = CascadeType.ALL 来允许持久化子元素。

@javax.persistence.Entity
@org.hibernate.annotations.Entity(dynamicUpdate = true)
@Table(name = "question_completion")
public class QuestionCompletion implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "question_completion_gen")
    @SequenceGenerator(name = "question_completion_gen", sequenceName = "question_completion_id_seq")
    @Column(name = "question_completion_id")
    private Long id;

    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "extended_question_id")
    protected List<QuestionCompletionAnswer> answers;
}

这是我的班级 - QuestionCompletionAnswer 班级的主键。

@Embeddable
public class QuestionCompletionAnswerPK implements Serializable {

    @Column(name = "question_completion_id")
    protected Long questionCompletionId;

    @Column(name = "extended_question_id")
    protected Long extendedQuestionId;
}

这是使用我的EmbeddedId 的课程。属性questionCompletionId 和questionCompletionId 是其他一些实体的外键，所以我还用@MapsId 注释将这些实体的整个对象放在了下面。

@javax.persistence.Entity
@org.hibernate.annotations.Entity(dynamicUpdate = true)
@Table(name = "extended_question_answer")
public class QuestionCompletionAnswer implements Serializable {

    @EmbeddedId
    private QuestionCompletionAnswerPK id;

    @ManyToOne
    @MapsId(value = "questionCompletionId")
    @JoinColumn(name = "question_completion_id", nullable = false, insertable = false, updatable = false)
    protected QuestionCompletion questionCompletion;

    @ManyToOne
    @MapsId(value = "extendedQuestionId")
    @JoinColumn(name = "extended_question_id", nullable = false, insertable = false, updatable = false)
    protected ExtendedQuestion extendedQuestion;
}

您能告诉我我的注释是否正确吗？也许我混合了几种方法。或者在这种情况下，我不能将我的基本对象及其所有子元素持久化。

编辑

现在我的映射看起来像：

@javax.persistence.Entity
@org.hibernate.annotations.Entity(dynamicUpdate = true)
@Table(name = "question_completion")
public class QuestionCompletion implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "question_completion_gen")
    @SequenceGenerator(name = "question_completion_gen", sequenceName = "question_completion_id_seq")
    @Column(name = "question_completion_id")
    private Long id;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "questionCompletion")
    protected List<QuestionCompletionAnswer> answers;
}

QuestionCompletionAnswerPK 类的代码相同。

@javax.persistence.Entity
@org.hibernate.annotations.Entity(dynamicUpdate = true)
@Table(name = "extended_question_answer")
public class QuestionCompletionAnswer implements Serializable {

    @EmbeddedId
    private QuestionCompletionAnswerPK id;

    @ManyToOne(cascade = CascadeType.PERSIST)
    @MapsId(value = "questionCompletionId")
    @JoinColumn(name = "question_completion_id", nullable = false)
    protected QuestionCompletion questionCompletion;

    @ManyToOne
    @MapsId(value = "extendedQuestionId")
    @JoinColumn(name = "extended_question_id", nullable = false)
    protected ExtendedQuestion extendedQuestion;
}

使用该映射，我仍然遇到相同的异常。

编辑 #2 但是，当我以这种方式更改 QuestionCompletionAnswer 类时：

@javax.persistence.Entity
@org.hibernate.annotations.Entity(dynamicUpdate = true)
@Table(name = "extended_question_answer")
public class QuestionCompletionAnswer implements Serializable {

    @EmbeddedId
    private QuestionCompletionAnswerPK id;

    @ManyToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "question_completion_id", nullable = false, insertable = false, updatable = false)
    protected QuestionCompletion questionCompletion;

    @ManyToOne
    @JoinColumn(name = "extended_question_id", nullable = false, insertable = false, updatable = false)
    protected ExtendedQuestion extendedQuestion;
}

我得到了那个例外：

Caused by: org.hibernate.id.IdentifierGenerationException: null id generated 
for:class com.example.model.domain.QuestionCompletionAnswer

Answer 1

编辑 1 和 2 仍然不正确。您需要在关系上指定 mapid，或者您必须自己在嵌入的 id 中设置字段值。并且当您使用 mapid 时，您不应该将连接列标记为 insertable=false，否则 jpa 无法为您插入值。我看到的最后一个问题是新问题没有持久化，因此它没有分配答案可以引用的 id - 您需要在 for 循环中显式保留新问题或将答案中的关系标记为级联持续存在。

Answer 2

为什么要混合 jpa 和 hibernate 注释？仅 jpa 注释就足够了。 尝试使用以下映射（我删除了 QuestionCompletionAnswerPK 类）：

QuestionCompletion.java

@Entity
@Table(name = "question_completion")
public class QuestionCompletion {

    @Id
    @SequenceGenerator(name = "question_completion_gen", sequenceName = "question_completion_id_seq")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "question_completion_gen")
    @Column(name = "question_completion_id")
    private Long id;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "questionCompletion")
    protected List<QuestionCompletionAnswer> answers;
}

QuestionCompletionAnswer.java

@Entity
@Table(name = "extended_question_answer")
public class QuestionCompletionAnswer implements Serializable {

    @Id
    @ManyToOne
    @JoinColumn(name = "question_completion_fk")
    private QuestionCompletion questionCompletion;

    @Id
    @ManyToOne
    @JoinColumn(name = "extended_question_fk")
    private ExtendedQuestion extendedQuestion;
}

通过这个映射，我运行了以下测试用例并且它工作了：

QuestionCompletion questionCompletion = new QuestionCompletion();
ExtendedQuestion extendedQuestion = new ExtendedQuestion();
QuestionCompletionAnswer answer = new QuestionCompletionAnswer();
answer.setQuestionCompletion(questionCompletion);
answer.setExtendedQuestion(extendedQuestion);
questionCompletion.setAnswers(Collections.singletonList(answer));
...
session.save(extendedQuestion);
session.save(questionCompletion);