MappedSuperclass - Change SequenceGenerator in Subclass

Question

I'm using JPA2 with Hibernate and try to introduce a common base class for my entities. So far it looks like that:

@MappedSuperclass
public abstract class BaseEntity {

    @Id
    private Long id;

    @Override
    public int hashCode() {
        // ...
    }

    @Override
    public boolean equals(Object obj) {
        // ...
    }

    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }
}

However, for every table theres a sequence $entityname_seq which I want to use as my sequence generator. How can I set that from my subclass? I think I need to override @GeneratedValue and create a new SequenceGenerator with @SequenceGenerator.

Countrified

Answer 1

Yes, it is possible. You can override the default generator name with the @SequenceGenerator annotation.

• Base class

    @MappedSuperclass
    public abstract class PersistentEntity implements Serializable
    {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "default_gen")
        protected Long id = 0L;

        public Long getId()
        {
            return id;
        }

        public void setId(Long id)
        { 
            this.id = id;
        }
    }

• Sequence (SQL)

  create sequence role_seq;

• Derived class

    @Entity
    @Table(name = "role")
    @SequenceGenerator(name = "default_gen", sequenceName = "role_seq", allocationSize = 1)
    public class Role extends PersistentEntity implements Serializable
    {
        private static final long serialVersionUID = 1L;

        @NotNull
        @Size(max = 32)
        private String name;

        public String getName()
        {
             return name;
        }

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

• This approach worked fine in Hibernate 4.1.x, but it didn't in EclipseLink 2.x.

edit

• As per the comment, it seems to be working with EclipseLink 2.6.1-RC1.

Comb

I've tested with EclipseLink 2.6.1-RC1 and it worked too. – Knotts

That's great news. Thank you! I'm gonna edit the answer. – Comb

An addition all subclasses must have the @SequenceGenerator defined otherwise errors will be thrown for the mapping – Turtledove

This is an incorrect solution. It will only work as long as you only have one sub-class of PersistentEntity. Say you create entity "Group" which also extends PersistentEntity. You'll then get error because Sequence Generator default_gen is defined twice within the same Persistency Unit. (EclipseLink 2.6.2) – Macswan

@Macswan Please check the full post, see the bottom lines. At the time it was answered it worked with hibernate but didn't even worked with EclipseLink and there is an edit later. It seemed to solve the OP's problem as well as for many other users. I'm sorry it didn't work for you. Feel free to contribute with you solution. – Comb

@rbento. Point taken. Yes, I should have said it is a no-longer-working solution in today's world and with recent EclipseLink. It may still be working fine with Hibernate, dunno. I don't doubt it have worked in the past. I'm afraid I haven't found a decent solution myself with EclipseLink. – Macswan

Indeed as specified by JEE-7 "The scope of the generator name is global to the persistence unit (across all generator types)." So even if it works at some time with some implementations it is not standard behavior. – Claman

Unlike some noted here, it works for me with Spring Boot JPA and Hibernate. See my long answer here: https://mcmap.net/q/271209/-mappedsuperclass-change-sequencegenerator-in-subclass – Kaohsiung

Does this work for IDENTITY strategy? – Alcinia

As for hibernate 5.4 this solution also does not work. – Transformer

@AleksandrSavvopulo - It does still work for me with hibernate 5.6.10. – Terbium

Answer 2

In JPA that cannot be done with annotations. Annotation itself cannot be overridden. Entity inherits all the mapping information from MappedSuperClass. There is only two annotations that can be used to redefine mappings inherited from mapped superClass:

1. AttributeOverride to override column mappings and
2. AssociationOverride to override join columns / table.

Neither of them helps with GeneratedValue.

Rundown

Answer 3

With EclipseLink, you can use a Customizer. DescriptorCustomizer interface defines a way to customize all the information about a jpa descriptor (aka a persistent entity).

public class SequenceCustomizer implements DescriptorCustomizer {

    @Override
    public void customize(ClassDescriptor descriptor) throws Exception {
        descriptor.setSequenceNumberName(descriptor.getTableName());
    }
}

and in your mapped superclass:

@MappedSuperclass
@Customizer(SequenceCustomizer.class)
public abstract class AbstractEntity implements Serializable {
    ...
}

Tennessee

Answer 4

I'm writing this as it gets too unreadable as the comment on the accepted answer:

I have a BaseEntity that every other Entity inherits from:

BaseEntity.java:

@MappedSuperclass
public abstract class BaseEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQ_ID")
    private Long id;

I then have two Entities User and Order that both inherit from BaseEntity whilst also having the @SequenceGenerator annotation:

User.java:

@SequenceGenerator(name = "SEQ_ID", sequenceName = "SEQ_USER", allocationSize = 1)
public class User extends BaseEntity { ... }

Order.java:

@SequenceGenerator(name = "SEQ_ID", sequenceName = "SEQ_ORDER", allocationSize = 1)
public class Order extends BaseEntity { ... }

It works on H2 at least with 2 Sequences SEQ_USER and SEQ_ORDERS:

select SEQ_USER.nextval from dual;
select SEQ_ORDERS.nextval from dual;

Ullyot

It works for multiple inherited entities, because Hibernate 5.18.3++ is tolerant by default. But you get warnings during startup: org.hibernate.boot.internal.InFlightMetadataCollectorImpl - HHH000069: Duplicate generator name SEQ_ID. See also hibernate.atlassian.net/browse/HHH-12454. If you get annoyed by the warnings, have a look at: stackoverflow.com/questions/5257921/#5258090 – Indicia