Spring Data JPA inheritance in repositories

Ideally, the following set up should work:

Entity classes

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class Equipment { ... }

@Entity
public class Crane extends Equipment {}

@Entity
public class Excavator extends Equipment {}

Repository interface

public interface EquipmentRepository<T extends Equipment> extends CrudRepository<T> {}

Repository consumer

@Service
public class SomeService {
  @Autowired
  private EquipmentRepository<Crane> craneRepository;

  @Autowired
  private EquipmentRepository<Excavator> excavatorRepository;
}

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I have set up a sample project on Github to demonstrate this in action. Running Maven tests as any of the following will show passing tests to demonstrate that the set up works as expected.

mvn test -Dspring.profiles.active="default,eclipselink"

mvn test -Dspring.profiles.active="default,openjpa"

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That said, this set up may not work with Hibernate, which is what I suspect you are using. Hibernate does not support auto-incremented identifier columns with TABLE_PER_CLASS inheritance. Therefore, attempting to run the set up above with Hibernate will throw an exception. This can be verified by running the following on the sample linked above.

mvn test -Dspring.profiles.active="default,hibernate"

You will have to create repository for each class. However you can keep your methods in the abstract. You'll need to provide @Query on each of the methods and use SpeL(Spring Expression Language) to add the type to the queries.

@NoRepositoryBean
public interface AbstractRepository<T extends AbstractEquipment> 
        extends CrudRepository<T, Long>{

 @Query("select e from #{#entityName} as e from equipment where e.name = equipmentName")
 T findEquipmentByName(String equipmentName);

}

Then extend like the following

@Transactional
public interface SpecialEquipmentRepo extends AbstractRepository<SpecialEquipment,Long>{

}