在Hibernate中使用注释映射多级继承 [英] Mapping multi-Level inheritance in Hibernate with Annotations

问题描述

以这个问题中列出的情况为例：

在Hibernate中映射多级继承

这个映射如何与Annotations而不是hbm文件一起完成？

解决方案

你有什么特别的麻烦？映射类层次通过加入的子类是非常简单：

pre $ @Entity
@Inheritance（strategy = InheritanceType.JOINED）
public class A implements可序列化{...}

@实体
公共类B扩展A {...}

@实体
@PrimaryKeyJoinColumn（name = A_ID）
public class C extends A {...}

@Entity
@PrimaryKeyJoinColumn（name =B_ID）
public class D extends B { ...}


---

更新（基于Michal的评论）。

如果你确实想使用鉴别符（你应该有一个 good 的理由） ），可以通过混合 table-每级分层策略 辅助表：

  @Entity 
 @Table（name =A_table）
 @Inheritance（strategy = InheritanceType.SINGLE_TABLE）
 @DiscriminatorColumn（name =entity_type）
 @DiscriminatorValue（A）
 public class A implements Serializable {...} 
 
 @Entity 
 @SecondaryTable（name =B_table）
 public class B extends A {...} 
 
 @Entity 
 @SecondaryTable（name =C_table，pkJoinColumns = { 
 @PrimaryKeyJoinColumn（name =A_ID，referencedColumnName =ID）
））
 public class C extends A {...} 
 
 @Entity 
 @SecondaryTable（name =D_table，pkJoinColumns = {
 @PrimaryKeyJoinColumn（name =B_ID，referencedColumnName =ID）
））
 public class D extends B { ...} 
  

这种方法的缺点是您必须为每个表格明确指定映射的属性：

  public class D extends B {
 @Column（table =D_table）
 private String someProperty; 
 
 ... 
} 
  

Take the situation listed in this question:

Mapping multi-Level inheritance in Hibernate

How would this mapping be done with Annotations rather than an hbm file?

解决方案

What specifically are you having trouble with? Mapping class hierarchy via joined subclasses is pretty straightforward:

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class A implements Serializable { ... }

@Entity
public class B extends A { ... }

@Entity
@PrimaryKeyJoinColumn(name="A_ID")
public class C extends A { ... }

@Entity
@PrimaryKeyJoinColumn(name="B_ID")
public class D extends B { ... }

---

Update (based on Michal's comment).

In case you do want to use discriminators (and you should have a good reason to do so), it's possible to do so by mixing table-per-class-hierarchy strategy with secondary tables:

@Entity
@Table(name="A_table")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="entity_type")
@DiscriminatorValue("A")
public class A implements Serializable { ... }

@Entity
@SecondaryTable(name="B_table")
public class B extends A { ... }

@Entity
@SecondaryTable(name="C_table", pkJoinColumns={
    @PrimaryKeyJoinColumn(name="A_ID", referencedColumnName="ID")
))
public class C extends A { ... }

@Entity
@SecondaryTable(name="D_table", pkJoinColumns={
    @PrimaryKeyJoinColumn(name="B_ID", referencedColumnName="ID")
))
public class D extends B { ... }

The downside to this approach is you'll have to explicitly specify the table for each property mapped:

public class D extends B {
  @Column(table="D_table")
  private String someProperty;

  ...
}

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