JPA : Entity extend with entity

Question

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

}

I tried this way Extend JPA entity to add attributes and logic

but I got this exception

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

Update 1

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

The entity has no primary key attribute defined

The Id must be specified in the base Entity, and it isn't in your example. The only time you can omit the Id from the base class would be when it is a MappedSuperclass. Inheritance defines the table used for a class in an inheritance relation, not just specifying the Table! — Neil Stockton, Jan 28 '16 at 07:35

Neil McGuigan · Answer 1 · 2016-01-28T22:09:49.653

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.

Code:

@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 {

}

I still got this error `org.hibernate.mapping.SingleTableSubclass cannot be cast to org.hibernate.mapping.RootClass` — Mrye, Jan 28 '16 at 04:16

score -1 · Answer 2 · answered Jan 28 '16 at 09:03

Any basic JPA docs would describe inheritance, discriminators and use of @Id.

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="DISCRIM", discriminatorType=DiscriminatorType.STRING)
@DiscriminatorValue("User")
@Table(name="users")
@NamedQuery(name="User.findAll", query="SELECT u FROM User u")
public class User implements Serializable{
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;

    private String name;
}

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

}

If you think that the existing documentation is enough, just add a comment to the post. If you think that it is necessary to add an answer, you should better document what you are suggesting. — Ward Clark, Oct 24 '20 at 14:25

JPA : Entity extend with entity

2 Answers2

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