Spring JPA native query with Projection gives "ConverterNotFoundException"

The query should be using a constructor expression:

@Query("select new com.example.IdsOnly(t.id, t.otherId) from TestTable t where t.creationDate > ?1 and t.type in (?2)")

And i dont know Lombok, but make sure there is a constructor that takes the two IDs as parameters.

with spring data you can cut the middle-man and simply define

public interface IdsOnly {
  Integer getId();
  String getOtherId();
}

and use a native query like;

@Query(value = "Id, OtherId from TestTable where CreationDate > ?1 and Type in (?2)", nativeQuery = true)
    public Collection<IdsOnly> findEntriesAfterDate(Date creationDate, List<Integer> types);

check out https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#projections