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.
Yes, it is possible. You can override the default generator name with the @SequenceGenerator
annotation.
@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;
}
}
edit
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:
Neither of them helps with GeneratedValue.
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 {
...
}
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;
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