Cascading save Entity objects with Foreign Key as a part of composite Primary Key

Question

I would like to persist object of my QuestionCompletion class with all child elements. One of these childs has a composite primary key. And as a part of this primary key I have also foreign key to another entity. As a result I am getting this error:

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

And the last "caused by" is of course NullPointerException:

Caused by: java.lang.NullPointerException

This is part of my code. The last line causes error.

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);

This is my basic entity class I would like to persist with all its childs elements. I have realized that List<QuestionCompletionAnswer> causes problems. I have used cascade = CascadeType.ALL to allow to persist childs elements also.

@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;
}

This is my class - Primary Key for the QuestionCompletionAnswer class.

@Embeddable
public class QuestionCompletionAnswerPK implements Serializable {

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

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

And this is class which uses my EmbeddedId. Attribues questionCompletionId and questionCompletionId are the foreign key for some another entities so I have placed below also whole objects of these entities with @MapsId annotation.

@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;
}

Could you tell me if my annotations are correct? Maybe I have mixed up few approaches. Or I can't in that case persist my basic object with all of its child elements.

EDIT

Now my mapping looks like:

@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;
}

Code of the QuestionCompletionAnswerPK class is the same.

@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;
}

With that mapping I am still getting the same exception.

EDIT #2 However when I have changed QuestionCompletionAnswer class in this way:

@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;
}

I am getting that exception:

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

Answer 1

Edit 1 and 2 are still not right. You need mapsid specified on the relationship or you must set the field in the embedded id with a value yourself. And when you use mapsid, you shouldn't have the join column marked insertable=false or jpa can't insert a value for you. The last problem I see is that the new question is not persisted so it doesn't get an id assigned that the answer can reference - you need to explicitly persist the new question in the for loop or mark the relationship in the answer to it to cascade persist.