使用@MappedSuperclass注释的类上的@SequenceGenerator

Question

I have following structure of my entities:

@MappedSuperclass
public abstract class BaseEntity {
  @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seqGenerator")
  private Long id;
}

@MappedSuperclass
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@SequenceGenerator(name = "seqGenerator", sequenceName = "DICTIONARY_SEQ")
public abstract class Intermed extends BaseEntity {}

@Entity
public class MyEntity1 extends Intermed {}

@Entity
public class MyEntity2 extends Intermed {}

And I got following exception:

    Caused by: org.springframework.beans.factory.BeanCreationException: 
Error creating bean with name 'sessionFactory' defined in class path resource [context/applicationContext.xml]: 
Invocation of init method failed; nested exception is org.hibernate.AnnotationException: Unknown Id.generator: seqGenerator

When I change @MappedSuperclass to @Entity on Intermed class, everything works OK. Are there any problems with using @MappedSuperclass and @SequenceGenerator? Or I have missed something?

Answer 1

I ran into the same problem described in this question while trying to achieve application wide id generators.

The solution is actually in the first answer: put the sequence generator on the primary key field .

Like so:

@MappedSuperclass
public abstract class BaseEntity {
  @Id
  @SequenceGenerator(name = "seqGenerator", sequenceName = "DICTIONARY_SEQ")
  @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seqGenerator")
  private Long id;
}

@MappedSuperclass
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public abstract class Intermed extends BaseEntity {}

@Entity
public class MyEntity1 extends Intermed {}

@Entity
public class MyEntity2 extends Intermed {}

While doing things this way seems remarkably stupid (at least to me) it does work.

Answer 2

Here is what the JPA 1.0 spec says about the SequenceGenerator annotation:

9.1.37 SequenceGenerator Annotation

The SequenceGenerator annotation defines a primary key generator that may be referenced by name when a generator element is specified for the GeneratedValue annotation. A sequence generator may be specified on the entity class or on the primary key field or property . The scope of the generator name is global to the persistence unit (across all generator types).

And a mapped superclass is not an entity. So according to the way I read the spec, what you want to do is not possible. Either make the Intermed class an entity or put the SequenceGenerator on the sub classes.