JPA:实体随实体扩展 [英] JPA : Entity extend with entity

问题描述

如何将一个实体扩展到另一个实体，但它们都引用同一张表?是否有可能 ?结构是这样的:

How can I extend an entity with another entity but both of them referring to the same table ? Is it possible ? The structure is something like this :

@Entity
@Table(name = "users")
@NamedQuery(name="User.findAll", query="SELECT u FROM User u")
public class User implements Serializable{
    private int id;
    private String name;
}

@Entity
@Table(name = "users")
@NamedQuery(name="SubUser.findAll", query="SELECT su FROM SubUser su")
public class SubUser extends User {

    @Override
    @Id  
    @GeneratedValue(strategy=GenerationType.AUTO)
    public int getId() {
      return super.getId();
    }

    //- Other fields and getter setter

}

我以这种方式尝试了扩展JPA实体以添加属性和逻辑

但是我遇到了这个异常

org.hibernate.mapping.SingleTableSubclass cannot be cast to org.hibernate.mapping.RootClass

更新1

我已经为子用户放置了@Id，因为@Entity显示了此异常

I already put the @Id for the SubUser because the @Entity shows this exception

The entity has no primary key attribute defined

推荐答案

• 将@Inheritance注释添加到超类
• 实现可序列化
• 为id添加一个吸气剂(您不一定需要一个setter)
• id应该是Integer，而不是int，以便您可以用null表示未分配的ID.
• Add the @Inheritance annotation to the super class
• Implement Serializable
• Add a getter for id (you don't need a setter necessarily)
• id should be Integer, not int, so that you can represent unassigned ids with null.

代码:

@Entity
@Table(name = "users")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class User implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id  
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Integer id;

    private String name;

    public Integer getId() {
      return id;
    }

    public String getName() {
      return name;
    }

    public void setName(String name) {
      this.name = name;
    }
}


@Entity
public class SubUser extends User {

}

这篇关于JPA:实体随实体扩展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！