How to check if a database entry exists using HQL description - sql

Question

The JpaRepository allows for executing some SQL queries without having to specify these specifically. For example, it is possible to execute the following method: myRepository.existsById(id).
I would like to execute this method, but instead of checking for the existence of the id, I would like to check for a different property, which I call employeeId. I am aware that I will have to specify this query; this is what I have tried:
#Query("SELECT 1 FROM MyTable t WHERE t.employeeId = ?1")
Integer existsByEmployeeId(Long id);
I am calling this method just before executing a DELETE query:
public Long deleteEntryByEmployeeId(Long id) {
if (myRepository.existsByEmployeeId(id) == 1) {
myRepository.deleteEntryByEmployeeId(id);
return id;
}
return null;
}
This doesn't really work as expected though, as I am returned the error:
Cannot invoke "java.lang.Integer.intValue()" because the return value of "myRepository.existsByEmployeeId(java.lang.Long)" is null
I understand that myRepository.existsByEmployeeId(id) returns null. This seems to be the case if there is no entry in myTable for the specified id. Anyways, I am looking for a smooth solution to this problem. Can somebody help?

Answer 1

There are multiple approaches.
You want to stick with declarative #Query annotation.
#Query("SELECT CASE WHEN count(t) = 1 THEN TRUE ELSE FALSE END FROM MyTable t WHERE t.employeeId = ?1")
Integer existsByEmployeeId(Long id);
It's OK to implement custom functionality.
public interface CustomEmployeeRepository {
boolean existsByEmployeeId(Long id);
}
#Repository
#Transactional(readOnly = true)
class CustomEmployeeRepository implements CustomEmployeeRepository {
#PersistenceContext
private EntityManager em;
#Override
boolean existsByEmployeeId(Long id) {
List list = em.createQuery("SELECT 1 FROM MyTable t WHERE t.employeeId = :id")
.setParameter("id", id)
.getResultList();
return list.size() == 1;
}
}
// inject EmployeeRepository and call existsByEmployeeId as usual
public interface EmployeeRepository extends JpaRepository<Employee, Long>, CustomEmployeeRepository {
}