What is the LIMIT clause alternative in JPQL?

Question

I\'m working with PostgreSQL query implementing in JPQL.

This is a sample native psql query which works fine,

SELECT * FROM students ORDER BY id DESC         


        

Answer 1

JPQL does not allow to add the limit keyword to the query generated by the HQL. You would get the following exception.

org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: LIMIT near line 1

But don't worry there is an alternative to use the limit keyword in the query generated by the HQL by using the following steps.

Sort.by(sortBy).descending() // fetch the records in descending order

pageSize = 1 // fetch the first record from the descending order result set.

Refer the following service class

Service:

@Autowired
StudentRepository repository; 

public List getLastStudentDetails(Integer pageNo, Integer pageSize, String sortBy)
{
    Integer pageNo = 0;
    Integer pageSize = 1;
    String sortBy = "id";
    Pageable paging = PageRequest.of(pageNo, pageSize, Sort.by(sortBy).descending());

    Slice pagedResult = repository.findLastStudent(paging);

    return pagedResult.getContent();
}

Your repository interface should implement the PagingAndSortingRepository

Repository:

public interface StudentRepository extends JpaRepository, PagingAndSortingRepository{

    @Query("select student from Student student")
    Slice findLastStudent(Pageable paging);
}

This will add the limit keyword to you query which you can see in the console. Hope this helps.