Spring boot JPA native query and pagination using countQuery - spring-boot

Question

I saw this example for native query which use countQuery:
public interface UserRepository extends JpaRepository<User, Long> {
#Query(value = "SELECT * FROM USERS WHERE LASTNAME = ?1 ORDER BY ?#{#pageable}",
countQuery = "SELECT count(*) FROM USERS WHERE LASTNAME = ?1",
nativeQuery = true)
Page<User> findByLastname(String lastname, Pageable pageable);
}
And the second example:
public interface UserRepository extends JpaRepository<User, Long> {
#Query(value="SELECT * FROM USERS WHERE LASTNAME = ?1", nativeQuery=true)
Page<User> findByLastname(String lastname, Pageable pageable);
}
The second example does not use countQuery, so what in the best practice? Can you explain ?
I tried both and both work well. What is the best practice ?

Answer 1

You can omit it if it is the same as your original query.
From the documentation :
countQuery
Defines a special count query that shall be used for pagination queries to lookup the total number of elements for a page. If none is configured we will derive the count query from the original
query or countProjection() query if any.
countQuery is useful when you need a different query to compute total items (this should almost never be the case though).
Note that countQuery can also be needed when you have a Pageable along with a non-native query, and need to fetch lazy loaded associations.
For example, let's assume your User entity has a lazy loaded registrations association :
This will not compile (query validation should fail with the below error message) :
#Query(value = "select u from Users u left join fetch u.registrations where lastName = ?1")
Page<User> findByLastname(String lastname, Pageable pageable);
org.hibernate.query.SemanticException: query specified join fetching,
but the owner of the fetched association was not present in the select
list
This will work :
#Query(value = "select u from Users u left join fetch u.registrations where lastName = ?1",
countQuery = "select u from Users u left join fetch u.registrations where lastName = ?1")
Page<User> findByLastname(String lastname, Pageable pageable);
(Note that you could have used #EntityGraph in that later case, this is just to demonstrate a use case of the countQuery where it is required).