jpa hibernate复合外键映射 [英] jpa hibernate composite foreign key mapping

问题描述

我无法为某些实体设置jpa映射。

I am having trouble setting up jpa mappings for some entities. I have a parent entity defined like the following.

@Entity
@Table(name="EIF_INSTANCE_HDR")
public class InstanceEntity implements Serializable{

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(generator="eif_inst_gen")
@SequenceGenerator(name="eif_inst_gen",sequenceName="EIF_INSTANCE_SEQ")
@Column(name = "EAIH_ID")
private Long eaihid;
@Column(name = "EAD_ID")
private Long eadid;

@OneToMany(targetEntity=InstanceNotifyEntity.class, mappedBy="instance",fetch=FetchType.EAGER, cascade = CascadeType.ALL)
private List<InstanceNotifyEntity> userDetails = new ArrayList<InstanceNotifyEntity>();
}

然后我有一个子实体w / a组合键和一个外键到这个表的主键如下：

I then have a child entity w/ a composite key, and a foreign key to the primary key of this table as follows:

@Entity
@Table(name="EIF_INST_NOTIFIED")
public class InstanceNotifyEntity implements Serializable{

private static final long serialVersionUID = 1L;

@Id
@ManyToOne
@JoinColumn(name="EAIH_ID", referencedColumnName="EAIH_ID")
private InstanceEntity instance;

@Id
@Column(name="USER_ID")
private Long userId;
@Column(name="COMMENT_TXT")
private String commentText;
}

我知道子实体是不正确的，但我不确定如何设置最多有一个复合PK。我知道我需要设置一个PK类，但我不知道如何做到这一点，当一个字段是父类的外键。一旦设置好，父母如何引用孩子实体？

I know the child entity is incorrect, but I am unsure how to set this up to have a composite PK. I know I need to setup a PK class, but I am not sure how to do that when one field is a foreign key to the parent class. And once that is setup how would the parent reference the child entity?

任何帮助都是值得赞赏的。 解决方案

Any help is appreciated.

这是由 JPA 2规范

解决方案

a>部分2.4.1，与派生身份对应的主键。该部分包含两个直接适用于您的问题的示例。

This is governed by JPA 2 spec section 2.4.1, "Primary Keys Corresponding to Derived Identities". The section contains two examples directly applicable to your problem.

正如规范中所述，在这种情况下，有两种方法可以表示子实体的键：

As described in the spec, there are two ways to represent the child entity's key in this case:

• @IdClass


• @EmbeddedId

• @IdClass
• @EmbeddedId

以下是 EmbeddedId EmbeddedId ，但是 IdClass 和 EmbeddedId 是重要的。您可以选择不同的方式。

Here's a rough sketch of the EmbeddedId way. I chose EmbeddedId arbitrarily, but the choice between IdClass and EmbeddedId is significant. You might choose differently.

// Child entity's composite primary key
@Embeddable
public class InstanceNotifyEntityId implements Serializable {
    Long eaihId;
    Long userId;
}

// Child entity
@Entity
@Table(name="EIF_INST_NOTIFIED")
public class InstanceNotifyEntity implements Serializable {
    @AttributeOverrides({
      @AttributeOverride(name="userId", column = @Column(name="USER_ID"))
      @AttributeOverride(name="eaihId", column = @Column(name="EAIH_ID"))
    })
    @EmbeddedId
    InstanceNotifyEntityId id;

    @MapsId("eaihId")
    @ManyToOne
    InstanceEntity instance;

    // ...
 }

父实体需要改变： userDetails 属性 mappedBy 应该是id.eaihId。我认为就是这样，但我之前没有使用过像这样的实体。可能错过了一些东西......如果您发现错误，请发帖。

The parent entity needs one change: the userDetails attribute mappedBy should be "id.eaihId". I think that's it, but I haven't used entities exactly like this before. Might have missed something... please post if you see errors.

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