Spring Data JPA inheritance in repositories

Question

I have an abstract class annotated with @MappedSuperClass. There are around 15 entities that extend this abstract class (having 15 corresponding tables in the database). The 15 entities all have the same attributes that are inherited from the abstract super class.

I have created a repository as below for the abstract class:

@NoRepositoryBean
public interface AbstractRepository <T extends AbstractClass, E extends Serializable>
                                    extends PagingAndSortingRepository<T, Serializable> {
  .....some methods here
}

The 15 entities/tables store some data (data pertaining to 15 separate equipment). Based on the equipment selected, the data from that table is to be retrieved. Will I have to create 15 separate repositories for the 15 concrete entities or is there any way to get the specific entity for the equipment selected using only the abstract repository? If repositories need to be created for each concrete entity, how to get the right repository for the specific equipment call? (store the table name and repository class in a map that gets created on startup of the application perhaps?)

score 20 · Answer 1 · answered Apr 13 '17 at 07:22

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;
}

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"

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"

score 16 · Accepted Answer · edited Jan 22 '20 at 18:14

16

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>{

}

edited Jan 22 '20 at 18:14

Leonardo Vieira

5
2

answered Apr 11 '17 at 16:16

Joseph McCarthy

305
2
7

Thanks @Joseph for the clarification. Since repositories for each equipment will need to be created, what is the better way of getting the repository instance for a specific equipment? One way is to autowire all the 15 repositories and have a switch case to use the correct repository instance based on the equipment passed (something like a factory to return the correct repository) – Prateek Mehra Apr 12 '17 at 02:13
1

I would avoid using a switch as this would have to be maintained, you could `@Autowire` a map where the key is the Type, and the value is the repository type. – Joseph McCarthy Apr 12 '17 at 07:23
The `@NoRepositoryBean` was crucial hint for working with repository inheritance, thanks! – Guillermo Jul 01 '20 at 21:12
Thanks for this. How would one go about joining additional tables when writing SpeL queries? – Robert Ngetich Dec 06 '21 at 16:13

Spring Data JPA inheritance in repositories

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