如何在休眠状态下不继承Id GeneratedValue（在子类中禁用@GeneratedValue）

Question

I have a hibernate entity Super Class:

@MappedSuperclass
public abstract class Pojo_Entity_SuperClass 
{
   @Id
   @GeneratedValue(strategy=GenerationType.IDENTITY)
   @Column(name="ID", unique=true, nullable=false, precision=18, scale=0)
   protected long id;
   public Long getId() {return id;}

   //Other entity fields and methods
}

Next I inherite other entity classes like this:

@Entity
@Table(name="USR")
public class Usr extends Pojo_Entity_SuperClass 
{
   //Columns, fileds and others
}

But in some cases I want to inherit entity with "id" field without @GeneratedValue annotation. The question is - how to disable @GeneratedValue annotation for id in child class ?

Answer 1

You can simply move the @Id from the base class to the sub-classes and then decide the generation strategies.

So you can have:

@MappedSuperclass
public abstract class Pojo_Entity_SuperClass 
{   
    public abstract Long getId();

    public abstract void setId(Long id);

    //Other entity fields and methods
}

@Entity
@Table(name="USR")
public class Usr extends Pojo_Entity_SuperClass {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="ID", unique=true, nullable=false, precision=18, scale=0)
    protected long id;  
}

@Entity
@Table(name="ADMIN")
public class Admin extends Pojo_Entity_SuperClass {
    @Id
    @SequenceGenerator(name = "ID_GENERATOR", sequenceName = "admin_id_seq")
    @GeneratedValue(generator = "ID_GENERATOR")
    @Column(name="ID", unique=true, nullable=false, precision=18, scale=0)
    protected long id;  
}

Is this what you need?

Answer 2

Alternatively, you perhaps actually don't want to avoid inheritance. I tried to do the same before I realized I wanted to create User entity with id from external system and force this id as id in my system. Since entities are otherwise created with our id, common ancestor with id and sequence generator is valid solution while User with external id would be nonsystematic.

Hence it was IMHO cleaner to generate id of User just as in any other case and add another column external_id to table and entity class.