JPQL left Join and Criteria API joins (Left and inner) throwing extra db queries to initialise associations - jpa-2.0

Question

I am having below two entities .Instructor entity has relationship oneToMany with Vehicle entity.
public class Instructor {
#Id
#GeneratedValue(strategy = GenerationType.AUTO, generator = "native")
#GenericGenerator(name = "native", strategy = "native")
private int id;
#Version
#Column(columnDefinition = "int(11) not null default 0")
private int version = 0;
#OneToMany(mappedBy = "instructor", orphanRemoval = true, cascade = CascadeType.ALL)
private Set<Vehicle> vehicles = new HashSet<>();
.....
public class Vehicle {
#Id
#GeneratedValue(strategy = GenerationType.AUTO, generator =
"native")
#GenericGenerator(name = "native", strategy = "native")
private int id;
#ManyToOne(fetch = FetchType.LAZY)
private Student student;
#ManyToOne(fetch = FetchType.LAZY)
private Instructor instructor;
I want to fetch all instructors along with their vehicles in one query .
I have tried below four ways for doing this but i am not able to do this with test case 2 , 3 and 4 .
Test Case 1 : With JPQL join fetch clause.
#Test
#Transactional
#Rollback(false)
public void fetchTest1(){
List<Instructor> instructorsJpqlJoinFetch = em
.createQuery("select distinct i from
Instructor i join fetch i.vehicles v ",
Instructor.class)
.getResultList();
print(instructorsJpqlJoinFetch);
}
private void print(List<Instructor> instructors) {
instructors.forEach(i -> {
System.out.println("######Instructor Name : " + i.getName());
i.getVehicles().forEach(v -> {
System.out.println("######Instructor Vehicle
Number : " + v.getVehicleNumber());
});
});
Db Query gone to DB for case 1 :
select
distinct instructor0_.id as id1_2_0_,
vehicles1_.id as id1_5_1_,
instructor0_.address as address2_2_0_,
instructor0_.birth_date_time as birth_da3_2_0_,
instructor0_.birth_date_time_zone_offset as birth_da4_2_0_,
instructor0_.created_date as created_5_2_0_,
instructor0_.day_off_time as day_off_6_2_0_,
instructor0_.day_start_time as day_star7_2_0_,
instructor0_.father_name as father_n8_2_0_,
instructor0_.mother_name as mother_n9_2_0_,
instructor0_.name as name10_2_0_,
instructor0_.photo as photo11_2_0_,
instructor0_.monthly_salary as monthly12_2_0_,
instructor0_.updated_date as updated13_2_0_,
instructor0_.version as version14_2_0_,
vehicles1_.creation_date as creation2_5_1_,
vehicles1_.instructor_id as instruct8_5_1_,
vehicles1_.purchased_date_time as purchase3_5_1_,
vehicles1_.purchased_date_zone_offset as purchase4_5_1_,
vehicles1_.student_id as student_9_5_1_,
vehicles1_.updated_date as updated_5_5_1_,
vehicles1_.vechicle_type as vechicle6_5_1_,
vehicles1_.vehicle_number as vehicle_7_5_1_,
vehicles1_.instructor_id as instruct8_5_0__,
vehicles1_.id as id1_5_0__
from
instructor instructor0_
inner join
vehicle vehicles1_
on instructor0_.id=vehicles1_.instructor_id
As a result All instructors are fethched from db along with their vehicles
and after executing i.getVehicles() no query goes to db again . Which should be a correct behaviour . I am getting this behaviour with JPQL join fetch clause .
Test Case 2 : Tried same with Criteria API like below :
#Test
#Transactional
#Rollback(false)
public void fetchTest3() {
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Instructor> cq =
cb.createQuery(Instructor.class);
Root<Instructor> root = cq.from(Instructor.class);
root.join(Instructor_.vehicles);
List<Instructor> instructorsWithCriteria =
em.createQuery(cq.distinct(true).select(root)).
getResultList();
print(instructorsWithCriteria);
}
Db query gone to db for case 2 :
select distinct instructor0_.id as id1_2_,
instructor0_.address as address2_2_,
instructor0_.birth_date_time as birth_da3_2_,
instructor0_.birth_date_time_zone_offset as birth_da4_2_,
instructor0_.created_date as created_5_2_,
instructor0_.day_off_time as day_off_6_2_,
instructor0_.day_start_time as day_star7_2_,
instructor0_.father_name as father_n8_2_,
instructor0_.mother_name as mother_n9_2_,
instructor0_.name as name10_2_,
instructor0_.photo as photo11_2_,
instructor0_.monthly_salary as monthly12_2_,
instructor0_.updated_date as updated13_2_,
instructor0_.version as version14_2_
from
instructor instructor0_
inner join
vehicle vehicles1_
on instructor0_.id=vehicles1_.instructor_id
**As a result all instructors are fethched from db . As soon as i hit
i.getVehciles() in print method a query to get vehicles of this instructor goes to db . Same happens for all instructors one by one .
Same behaviour happens for case 3 and 4 below too .
What should be passed in select clause of case 2, 3, 4 so that vehicle columns also got selected in query ?
**
Test case 3: JPQL left join
#Test
#Transactional
#Rollback(false)
public void fetchTest2() {
List<Instructor> instructorsJpqlLeftJoin = em
.createQuery("select distinct i from Instructor i left join
i.vehicles v ", Instructor.class)
.getResultList();
print(instructorsJpqlLeftJoin);
}
Db Query to db for Case 3 :
select
distinct instructor0_.id as id1_2_,
instructor0_.address as address2_2_,
instructor0_.birth_date_time as birth_da3_2_,
instructor0_.birth_date_time_zone_offset as birth_da4_2_,
instructor0_.created_date as created_5_2_,
instructor0_.day_off_time as day_off_6_2_,
instructor0_.day_start_time as day_star7_2_,
instructor0_.father_name as father_n8_2_,
instructor0_.mother_name as mother_n9_2_,
instructor0_.name as name10_2_,
instructor0_.photo as photo11_2_,
instructor0_.monthly_salary as monthly12_2_,
instructor0_.updated_date as updated13_2_,
instructor0_.version as version14_2_
from
instructor instructor0_
left outer join
vehicle vehicles1_
on instructor0_.id=vehicles1_.instructor_id
Case 4 : Criteria API Left Join :
#Test
#Transactional
#Rollback(false)
public void fetchTest4() {
CriteriaBuilder cbLeftJoin = em.getCriteriaBuilder();
CriteriaQuery<Instructor> cqLeftJoin =
cbLeftJoin.createQuery(Instructor.class);
Root<Instructor> rootLeftJoin = cqLeftJoin.from(Instructor.class);
rootLeftJoin.join(Instructor_.vehicles, JoinType.LEFT);
List<Instructor> instructorsWithCriteriaLeftJoin = em
.createQuery(cqLeftJoin.distinct(true).
select(rootLeftJoin)).getResultList();
print(instructorsWithCriteriaLeftJoin);
}
Db Query for case 4 :
select
distinct instructor0_.id as id1_2_,
instructor0_.address as address2_2_,
instructor0_.birth_date_time as birth_da3_2_,
instructor0_.birth_date_time_zone_offset as birth_da4_2_,
instructor0_.created_date as created_5_2_,
instructor0_.day_off_time as day_off_6_2_,
instructor0_.day_start_time as day_star7_2_,
instructor0_.father_name as father_n8_2_,
instructor0_.mother_name as mother_n9_2_,
instructor0_.name as name10_2_,
instructor0_.photo as photo11_2_,
instructor0_.monthly_salary as monthly12_2_,
instructor0_.updated_date as updated13_2_,
instructor0_.version as version14_2_
from
instructor instructor0_
left outer join
vehicle vehicles1_
on instructor0_.id=vehicles1_.instructor_id
What should i do in case 2,3,4 so that vehicles columns also got selected in the same query so that no secondory selects go to db?