使用Hibernate持久保存接口 [英] Persist collection of interface using Hibernate

问题描述

  @Entity 
 @Table（name =zoo ）
 public class Zoo {
 @OneToMany 
 private Set< Animal>动物=新的HashSet< Animal>（）; 
} 
 
 //只是一个标记界面
 public interface Animal {
} 
 
 @Entity 
 @Table（name =dog）
 public class Dog implements Animal {
 // ID和其他属性
} 
 
 @Entity 
 @Table（name = cat）
 public class Cat implements Animal {
 // ID和其他属性
} 
  

当我尝试坚持动物园时，Hibernate抱怨道：

 使用@OneToMany或@ManyToMany定位一个未映射的类：blubb.Zoo.animals [blubb.Animal] 
  

我知道 targetEntity - @property <@ c $ c> @OneToMany 但这意味着，只有狗或猫可以住在我的动物园里。

有没有什么办法可以用Hibernate持久化一个接口的集合，它有几个实现？

解决方案

JPA注释在接口上不受支持。从 Java持久化与Hibernate （p.210）：

请注意，JPA规范
doesn在界面上不支持任何映射注释
！这将在
规范的未来版本中解决
;当你阅读这本
的书时，可能会有
和Hibernate Annotations。

可能的解决方案是应该使用带有 TABLE_PER_CLASS 继承策略的抽象实体（因为您不能在关联中使用映射超类 - 它不是实体）。像这样：

  @Entity 
 @Inheritance（strategy = InheritanceType.TABLE_PER_CLASS）
 public abstract class AbstractAnimal {
 @Id @GeneratedValue（strategy = GenerationType.TABLE）
 private Long id; 
 ... 
} 
 
 @Entity 
 public class Lion extends AbstractAnimal implements Animal {
 ... 
} 
 
 @Entity 
 public class Tiger extends AbstractAnimal implements Animal {
 ... 
} 
 
 @实体
 public class Zoo {
 @Id @GeneratedValue 
私人长ID; 
 
 @OneToMany（targetEntity = AbstractAnimal.class）
 private Set< Animal>动物=新的HashSet< Animal>（）; 
 
 ... 
} 
  

但没有太多在保持IMO接口方面的优势（实际上，我认为持久化类应该是具体的）。

参考文献

• 注释，继承和接口


• 在一对多关系中使用MappedSuperclass


• 与MappedSuperclass的多态关联抛出异常

I want to persist my litte zoo with Hibernate:

@Entity
@Table(name = "zoo") 
public class Zoo {
    @OneToMany
    private Set<Animal> animals = new HashSet<Animal>();
}

// Just a marker interface
public interface Animal {
}

@Entity
@Table(name = "dog")
public class Dog implements Animal {
    // ID and other properties
}

@Entity
@Table(name = "cat")
public class Cat implements Animal {
    // ID and other properties
}

When I try to persist the zoo, Hibernate complains:

Use of @OneToMany or @ManyToMany targeting an unmapped class: blubb.Zoo.animals[blubb.Animal]

I know about the targetEntity-property of @OneToMany but that would mean, only Dogs OR Cats can live in my zoo.

Is there any way to persist a collection of an interface, which has several implementations, with Hibernate?

解决方案

JPA annotations are not supported on interfaces. From Java Persistence with Hibernate (p.210):

Note that the JPA specification doesn’t support any mapping annotation on an interface! This will be resolved in a future version of the specification; when you read this book, it will probably be possible with Hibernate Annotations.

A possible solution would be to use an abstract Entity with a TABLE_PER_CLASS inheritance strategy (because you can't use a mapped superclass - which is not an entity - in associations). Something like this:

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class AbstractAnimal {
    @Id @GeneratedValue(strategy = GenerationType.TABLE)
    private Long id;
    ...
}

@Entity
public class Lion extends AbstractAnimal implements Animal {
    ...
}

@Entity
public class Tiger extends AbstractAnimal implements Animal {
    ...
}

@Entity
public class Zoo {
    @Id @GeneratedValue
    private Long id;

    @OneToMany(targetEntity = AbstractAnimal.class)
    private Set<Animal> animals = new HashSet<Animal>();

    ...
}

But there is not much advantages in keeping the interface IMO (and actually, I think persistent classes should be concrete).

References

• Annotations, inheritance and interfaces
• using MappedSuperclass in relation one to many
• Polymorphic association to a MappedSuperclass throws exception

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