java – 级联将实体对象与外键一起保存为复合主键的一部分

我想坚持我的QuestionCompletion类的对象与所有子元素.其中一个孩子有一个复合主键.作为这个主键的一部分,我也有另一个实体的外键.结果我得到这个错误：

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

最后一个“由…引起”当然是NullPointerException：

Caused by: java.lang.NullPointerException

这是我的代码的一部分.最后一行会导致错误.

QuestionCompletion questionCompletion = new QuestionCompletion();
ListNown 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);

这是我的基本实体类,我想坚持其所有的子元素.我已经意识到List< QuestionCompletionAnswer>引起问题.我使用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

这是我的类 – QuestionCompletionAnswer类的主键.

@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的类.属性问题ComplempleId和questionCompletionId是某些其他实体的外键,所以我在下面还用@MapsId注释放置了这些实体的整个对象.

@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",updatable = false)
    protected ExtendedQuestion extendedQuestion;
}

你能告诉我我的注释是否正确吗？也许我混淆了一些方法.或者我不能在这种情况下坚持我的基本对象及其所有子元素.

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,sequenceName = "question_completion_id_seq")
    @Column(name = "question_completion_id")
    private Long id;

    @OnetoMany(cascade = CascadeType.ALL,mappedBy = "questionCompletion")
    protected List

QuestionCompletionAnswerPK类的代码是相同的.

@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;
}

通过该映射,我仍然得到相同的异常.

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",updatable = false)
    protected QuestionCompletion questionCompletion;

    @ManyToOne
    @JoinColumn(name = "extended_question_id",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

最佳答案

编辑1和2仍然不对.您需要在关系中指定的mapsid,或者您必须自己在嵌入式ID中设置值.当您使用mapsid时,您不应该将连接列标记为insertable = false或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,所以它没有得到答案可以引用的id – 你需要在for循环中明确地保留新问题或者在答案中标记关系到级联持续存在.