hibernate如何保存一对多/多对一的注解？（儿童不储蓄）答案

【问题标题】：How does hibernate save one-to-many / many-to-one annotations? (Children not saving)hibernate如何保存一对多/多对一的注解？（儿童不储蓄）
【发布时间】：2012-10-27 01:41:12
【问题描述】：

我继承了一个休眠应用程序，但遇到了问题。似乎代码并没有将孩子保存在一对多的关系中。它是双向的，但是在保存父对象时，它似乎并没有保存子对象。

在这种情况下，Question 类是父类。

// Question.java
@Entity
@SequenceGenerator(name = "question_sequence", sequenceName = "seq_question", allocationSize = 1000)
@Table(name = "question")
public class Question {
   protected Long questionId;
   protected Set<AnswerValue> answerValues;

   public TurkQuestion(){}

   public TurkQuestion(Long questionId){
      this.questionId = questionId;
   }

   @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "question_sequence")
   @Column(name = "question_id")
   public Long getQuestionId(){
      return questionId;
   }

   @OneToMany(fetch = FetchType.EAGER)
   @JoinColumn(name = "question_id",referencedColumnName="question_id")
   public Set<AnswerValue> getAnswerValues(){
      return answerValues;
   }

   public void setQuestionId(Long questionId){
      this.questionId = questionId;
   }

   public void setAnswerValues(Set<AnswerValue> answerValues){
      this.answerValues = answerValues;
   }
}

AnswerValue 是子类。

// AnswerValue.java
@Entity
@SequenceGenerator(name = "answer_value_sequence", sequenceName = "seq_answer_value", allocationSize = 1)
@Table(name = "answer_value")
public class AnswerValue {
    protected Long answerValueId;
    protected Question question;
    protected String answerValue;

    public AnswerValue(){}

    public AnswerValue(Long answerValueId, Long questionId, String answerValue){
       this.answerValueId = answerValueId;
       this.question = new Question(questionId);
       this.answerValue = answerValue;
    }

    @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "answer_value_sequence")
    @Column(name = "answer_value_id")
    public Long getAnswerValueId(){
       return answerValueId;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "question_id", nullable = false )
    public Question getQuestion(){
       return question;
    }

    @Column(name = "answer_value")
    public String getAnswerValue(){
       return answerValue;
    }

    public void setAnswerValueId(Long answerValueId){
       this.answerValueId = answerValueId;
    }

    public void setQuestion(Question question){
       this.question = question;
    }

    public void setAnswerValue(){
       this.answerValue = answerValue;
    }
}

还有 DAO：

// QuestionDao.java
public class QuestionDao {
   public void saveOrUpdateAll(List<Question> list){
      getHibernateTemplate().saveOrUpdateAll(list);
   }
}

似乎当我调用 saveOrUpdateAll 时，问题已保存，但作为 Question 对象子级的 AnswerValue 未保存。

有什么建议吗？

【问题讨论】：

标签： java hibernate annotations one-to-many many-to-one

【解决方案1】：

您需要手动完成或将级联属性添加到您的注释中，即Hibernate: Cascade Type

或Hibernate: How use cascade in annotation?

【讨论】：

【解决方案2】：

对于oneToMany关系，请将cascade映射注解定义为：

    Cascade={CascadeType.ALL}

或

     Cascade={ CascadeType.ALL, CascadeType.DELETE_ORPHAN }

在您的映射中：

    @ManyToOne(fetch = FetchType.EAGER, 
               cascade = { CascadeType.ALL, CascadeType.DELETE_ORPHAN })
    @JoinColumn(name = "question_id",referencedColumnName="question_id")
    public Set<AnswerValue> getAnswerValues(){
        return answerValues;
    }

【讨论】：

【解决方案3】：

如果问题和答案实体之间存在一对多关系，那么为什么要使用：

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "question_id",referencedColumnName="question_id")
public Set<AnswerValue> getAnswerValues(){
    return answerValues;
}

我认为你应该改用这个：

@OneToMany(fetch = FetchType.EAGER)
@JoinColumn(name = "question_id",referencedColumnName="question_id")
public Set<AnswerValue> getAnswerValues(){
    return answerValues;
}

【讨论】：