Distinct on specific column using JPA Specification - spring-boot

Question

I'm trying to write the following query using JPA Specification.
select distinct name from hcp where area = 'Dhaka';
select distinct name from hcp where area = 'Dhaka';
The hcp entity looks as following
#Entity
public class HCP implements Serializable {
#Id
#Column
private String id;
#Column
private String name;
#Column
private String area;
}
The table would look like this
I tried to convert the above query using jpa-specification as following. It's selecting 'name' field and I've set distinct as true
List<HCP> result = hcpRepository.findAll(new Specification<HCP>() {
#Override
public Predicate toPredicate(Root<HCP> root, CriteriaQuery<?> query, CriteriaBuilder criteriaBuilder) {
query.select(root.get("name")).distinct(true);
return criteriaBuilder.equal(root.get("area"), "Dhaka");
}
});
But it's not working. It's only applying district on the field that has #Id annotation. I want to apply distinct on area field.
Generated Hibernate Query looks like this:
select
distinct hcp0_.id as id1_0_,
hcp0_.area as area2_0_,
hcp0_.name as name3_0_
from
hcp hcp0_
where
hcp0_.area=?
How can I get generated query like the following?
select
distinct hcp0_.name as name3_0_
from
hcp hcp0_
where
hcp0_.area= 'Dhaka'
The desired result will list distinct names based on area.
How can I apply distinct on a specific field using JPA Specification?
Desired query and output:

Answer 1

You can't use Specifications because you want to return a List of Strings.
So you could use JPQL
#Query("select distinct h.name from Hcp h where area = 'Dhaka'")
List<String> findDistinctName();