JPA：如何使用@ElementCollection 注解？

Question

我需要你的帮助来映射 Hibernate 中两个表的关系，使用 @ElementCollection 注释。

第一个是父表
表名：父
数据库列

KEY1         Char      (first primary key field)
KEY2         Char      (second primary key field)
DESCRIPTION  Char
DEPENDENTID  BigInt

第二个是依赖表
表名：依赖
数据库列

PARENTID     BigInt    (first primary key field)
CODE         Char      (second primary key field)
FIELD1       Char
FIELD2       Char

我需要使用@EmbeddedId 注释为两个表定义PK， 所以我创建了两个类：

@Embeddable
public class ParentPK implements Serializable
{
   @Column(name="K1")
   private String iK1;
   @Column(name="K2")
   private String iK2;
  // I omit the constructor, getter, setter, equals, hashcode method 
}

@Embeddable
public class DependentPK implements Serializable
{
  @Column(name="PARENTID")
  private String iParentId;
  @Column(name="CODE")
  private String iCode;
  // I omit the constructor, getter, setter, equals, hashcode method 
}

然后我创建了两个 bean：
DEPENDENT 表的类。
请注意，在这个类中我不想有任何关系注释

@Entity
@Table(name = "DEPENDENT")
public class DependentBean implements Serializable
{
   @EmbeddedId
   private DependentPK iDependentPK;
   @Column(name = "FIELD1")
   private String iField1;
   @Column(name = "FIELD2")
   private String iField2;
   // I omit the constructor, getter, setter methods
}

还有 PARENT 表的类

@Entity
@Table(name = "PARENT")
public class ParentBean implements Serializable
{
   @EmbeddedId
   ParentPK iParentPK;
   @Column(name = "DESCRIPTION")
   private String iDescription;
   @Column(name = "DEPENDENTID")
   private long iDependentId;
   @ElementCollection
   @CollectionTable(name="DEPENDENT", joinColumns={@JoinColumn(name="PARENTID",  referencedColumnName="DEPENDENTID")})
   private Set<DependentBean> iDependentBeans = new HashSet<DependentBean>();
   // I omit the constructor, getter, setter methods
}

当我尝试部署时出现错误：

原因：org.hibernate.MappingException：外键 （FK9619C2A17B05CB2：依赖 [iDependentBeans_PARENTID,iDependentBeans_CODE])) 必须相同 作为引用的主键的列数（DEPENDENT [PARENTID,iDependentBeans_PARENTID,iDependentBeans_CODE])

所以我做错了什么，但我无法想象是什么。 有人愿意帮助我吗？

Answer 1

@ElementCollection 应与基本类型或可嵌入类一起使用，而不是用于实体。

DependentBean 是一个实体。

尝试使用一对多映射并修改您的架构

父架构

KEY1         Char      (PK)
KEY2         Char      (PK)
DEPENDENTID  BigInt    (PK)
DESCRIPTION  Char

依赖模式

CODE         Char      (PK)
PARENTID     BigInt    (FK)
KEY1         Char      (FK)
KEY2         Char      (FK)
FIELD1       Char
FIELD2       Char

一对多映射

父PK

@Embeddable
public class ParentPK {
    @Column(name = "K1")
    private String iK1;
    @Column(name = "K2")
    private String iK2;
    @Column(name = "DEPENDENTID")
    private long iDependentId;
}

父豆

@Entity
@Table(name = "PARENT")
public class ParentBean {
    @EmbeddedId
    ParentPK iParentPK;

    @OneToMany(mappedBy = "parent")
    List<DependentBean> iDependentBeans;
}

依赖豆

@Entity
@Table(name = "DEPENDENT")
public class DependentBean {
    @Id
    @Column(name = "CODE")
    private String iCode;

    @ManyToOne
    @JoinColumns({ 
      @JoinColumn(name = "PARENTID", referencedColumnName = "iDependentId"),  
      @JoinColumn(name = "K1", referencedColumnName = "iK1"),
      @JoinColumn(name = "K2", referencedColumnName = "iK2") })
    ParentBean parent;
}