JPA 2.0 Hibernate @OneToMany + @MapKeyJoinColumn [英] JPA 2.0 Hibernate @OneToMany + @MapKeyJoinColumn

问题描述

OneToMany + MapKeyJoinColumn不适用于我，请提出我做错了什么。

我使用JPA 2.0 + Hibernate 3.6.1
并且想映射下表：

---

---

到类：

---

  
 @实体
公共类问题{
 / / id和其他字段
 
 @OneToMany（mappedBy =question，cascade = CascadeType.ALL）
 @MapKeyJoinColumn（name =language_id）
 private Map< Language，语句> statement = 
 new HashMap< Language，Statement>（）; 
} 
 
 @实体
公共类语句{
 @Id 
私有长ID; 
 
 @ManyToOne 
 @JoinColumn（name =language_id，nullable = true）
 private语言语言; 
 
 @ManyToOne 
 @JoinColumn（name =question_id，nullable = false）
 private问题问题; 
 
 @Column（name =message）
 private String message; 
} 
 
 @Entity 
公共类语言{
 @Id 
私有长ID; 
 
 @Column（name =name）
私有字符串名称; 
} 
  

但它不起作用。 EntityManager持久保存它，但是当我检索Question时，在它的语句映射中只有一个语言到空的条目。
请帮忙

---

Edit1 ：奇怪，但是当我预载所有语言，如下所示：

  
 String sql =从语言l中选择l; 
 List languages = entityManager.createQuery（sql，Language.class）.getResultList（）; 
  

然后它就可以工作了！

是否有人知道如何让hibernate自动加载某些类的所有对象？

解决方案

实际上，您的类Statement中的id属性必须是复合主键。您的表语句中不需要statement_id。主键由language_id和question_id组成。

尝试：

  @Entity 
 public class Statement实现Serializable {
 
 private static final long serialVersionUID = 1L; 
 
 @EmbeddedId 
 private StatementId id = new StatementId（）; 
 
 @Column（name =message）
 private String message; 
} 
 
 @Embeddable 
 private static class StatementId implements Serializable {
 
 private static final long serialVersionUID = 1L; 
 
 StatementId（）{} 
 
 @ManyToOne 
 private问题产品; 
 
 @ManyToOne 
私人语言语言; 
 
 
  

不要忘记问题中的fetchType以避免
LazyInitializationExceptions

  public class Question {
 
 @OneToMany（mappedBy =id。问题，fetch = FetchType.EAGER）
 @MapKeyJoinColumn（name =language_id）
私人地图< Language，Statement> statements = new HashMap< Language，Statement>（）; 
} 
  

希望这会有所帮助。

OneToMany + MapKeyJoinColumn doesn't work for me, please suggest what I'm doing wrong.

I'm using JPA 2.0 + Hibernate 3.6.1 And want to map following tables:

---

---

To Classes:

---

@Entity
public class Question {
    // id and other fields

    @OneToMany(mappedBy="question", cascade = CascadeType.ALL)
    @MapKeyJoinColumn(name="language_id")
    private Map<Language, Statement> statements =
        new HashMap<Language, Statement>();
}

@Entity
public class Statement {
    @Id
    private Long id;

    @ManyToOne
    @JoinColumn(name = "language_id", nullable = true)
    private Language language;

    @ManyToOne
    @JoinColumn(name = "question_id", nullable = false)
    private Question question;

    @Column(name = "message")
    private String message;
}

@Entity
public class Language {
    @Id
    private Long id;

    @Column(name = "name")
    private String name;
}

But it doesn't work. EntityManager persists it correctly, but when I retrieve Question, in it's statements map there is only one language-to-null entry. Please, help

---

Edit1: Strange, but when I preload all Languages, like this:

String sql = "select l from Language l";
List languages = entityManager.createQuery(sql, Language.class).getResultList();

then it works!
Does anybody know how to make hibernate automatically load all objects of certain class?

解决方案

In fact, the id property in your class Statement must be a composite primary key. You do not need a statement_id in your table Statement. The primary key is composed of both language_id and question_id.

Try that :

    @Entity
    public class Statement implements Serializable {

        private static final long serialVersionUID = 1L;

        @EmbeddedId
        private StatementId id = new StatementId();

        @Column(name = "message")
        private String message;
    }

    @Embeddable
    private static class StatementId implements Serializable {

        private static final long serialVersionUID = 1L;

        StatementId(){}

        @ManyToOne
        private Question product;

        @ManyToOne
        private Language language;

    }

And do not forget the fetchType in Question in order to avoid LazyInitializationExceptions.

public class Question {

    @OneToMany(mappedBy="id.question", fetch=FetchType.EAGER)
    @MapKeyJoinColumn(name="language_id")
    private Map<Language, Statement> statements = new HashMap<Language, Statement>();
}

Hope it will help.

这篇关于JPA 2.0 Hibernate @OneToMany + @MapKeyJoinColumn的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！