How use generic entity name in JPQL

I have three tables with same column name and types, what changes is just the table name.

Example: | TABLE1 | TABLE2 | TABLE3 | | —— | —— | ——- | | ID | ID | ID | | NAME | NAME | NAME | | FOO | FOO | FOO | | BAR | BAR | BAR |

---

I have three entities, one to each table.

Entity Parent:

public class EntityParent {
    
    @Id
    @Column(name = "ID")
    private Long id;
    
    @Column(name = "NAME")
    private String name;
    
    @Column(name = "FOO")
    private String foo;
    
    @Column(name = "BAR")
    private String bar;
    
}

Entity Childs:

@Table(name = "TABLE1")
public class Entity1 extends EntityParent {
}

@Table(name = "TABLE2")
public class Entity2 extends EntityParent {
}

@Table(name = "TABLE3")
public class Entity3 extends EntityParent {
}

I have a generic repository, with some methods:

@NoRepositoryBean
public interface EntityGenericRepository<T extends EntityParent, ID> extends JpaRepository<T, ID> {

    List<T> findAllByName(String name);

    List<T> findAllByFooAndBar(String foo, String bar);

    List<T> findAllByNameOrFoo(String name, String foo);

}

So far so good. See code repetition below, with methods findEntityXToDto:

@Repository
public interface Entity1Repository extends EntityGenericRepository<Entity1, Long> {

    @Query("SELECT new com.package.MyDTO(e.foo, e.bar) FROM Entity1 e WHERE e.name = :name")
    List<MyDTO> findEntity1ToDto(@Param("name") String name);

}

@Repository
public interface Entity2Repository extends EntityGenericRepository<Entity2, Long> {

    @Query("SELECT new com.package.MyDTO(e.foo, e.bar) FROM Entity2 e WHERE e.name = :name")
    List<MyDTO> findEntity2ToDto(@Param("name") String name);

}

@Repository
public interface Entity3Repository extends EntityGenericRepository<Entity3, Long> {

    @Query("SELECT new com.package.MyDTO(e.foo, e.bar) FROM Entity3 e WHERE e.name = :name")
    List<MyDTO> findEntity3ToDto(@Param("name") String name);

}

It’s here problem. How create SELECT JPQL generic? Something as:

SELECT new com.package.MyDTO(t.foo, t.bar) FROM T t WHERE t.name = :name

Answer

Spring Data JPA release 1.4 supports the usage of restricted SpEL template expressions in manually defined queries that are defined with @Query. It supports a variable called entitiyName. It inserts the entityName of the domain type associated with the given repository. I would suggest using separate repositories and pass the SpEL there. For example:

Let you have a BaseEntity and other entities like TableOne, TableTwo and TableThree. All extends the BaseEntity and have the exact same attributes.

@MappedSuperclass
@Data
public class BaseEntity {
    @Id
    private String id;
    private String columnVal;
}

Create a base repository with @NoRepositoryBean annotation as it prevents spring to implement the repository on this base repository.

@NoRepositoryBean
public interface DemoRepository<T extends BaseEntity> extends JpaRepository<T, String> {
    @Query("select u from #{#entityName} u where u.columnVal = ?1")
    List<T> findByColumnVal(String columnVal);
}

Finally Implement your own repository based on each entity:

@Repository
public interface TableOneRepository extends DemoRepository<TableOne> {
    //add more methods if needed
}

And call this repository from the entity wise service class:

@Service
public class TableOneService {

    private final TableOneRepository repository;

    @Autowired
    public TableOneService(TableOneRepository repository) {
        this.repository = repository;
    }

    public List<TableOne> demoMethod(String val) {
        return this.repository.findByColumnVal(val);
    }

}

Now just call the method demoMethod and you’ll get result for TableOne entity. Implement exactly the same for the other entities. Hence you can solve your problem.