使用外鍵級聯保存實體對象作爲複合主鍵的一部分

Question

我想用我的QuestionCompletion類的所有子元素保持對象。其中一個孩子有一個複合主鍵。作爲這個主鍵的一部分，我還有另一個實體的外鍵。結果我收到此錯誤：

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 

而最後的「致」當然是NullPointerException的：

Caused by: java.lang.NullPointerException 

這是我的代碼部分。最後一行會導致錯誤。

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); 

這是我的基本實體類我想堅持所有的孩子元素。我意識到List<QuestionCompletionAnswer>會導致問題。我用cascade = CascadeType.ALL也允許堅持孩子的元素。

@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; 
} 

這是我的課 - QuestionCompletionAnswer類的主鍵。

@Embeddable 
public class QuestionCompletionAnswerPK implements Serializable { 

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

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

這是使用我的EmbeddedId的類。屬性questionCompletionId和questionCompletionId是另一些實體的外鍵，因此我也在下面將這些實體的整個對象與@MapsId註釋放在一起。

@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; 
} 

您能否告訴我我的註釋是否正確？也許我混合了幾種方法。或者我不能在這種情況下堅持我的基本對象與它的所有子元素。

編輯

現在我的映射是這樣的：

@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; 
} 

的QuestionCompletionAnswerPK類的代碼是一樣的。

@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; 
} 

有了這個映射，我仍然得到相同的異常。

編輯＃2 然而，當我以這種方式改變了QuestionCompletionAnswer類：

@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; 
} 

我得到這個異常：

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

Answer 1

編輯1,2仍然不正確。您需要在關係中指定mapsid，或者您必須使用您自己的值在嵌入ID中設置字段。並且，當您使用mapsid時，不應將加入列標記爲insertable = false，否則jpa不能爲您插入值。我看到的最後一個問題是，新問題沒有被保留，因此它沒有得到一個指定了答案可以引用的標識符 - 您需要明確地將新問題保留在for循環中，或者在答案中標記關係以級聯堅持。

Answer 2

爲什麼混合jpa和hibernate註釋？單獨的jpa註釋就足夠了。 與下面的映射嘗試（I除去類QuestionCompletionAnswerPK）：

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; 
} 

利用這種映射，我運行以下測試用例和它的工作：

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);