Hibernate Criteria FetchMode.JOIN is doing lazy loading - spring-boot

Question

I have a paginated endpoint which internally uses Hibernate Criteria to fetch certain objects and relations. The FetchMode is set as FetchMode.JOIN.
When I am trying to hit the endpoint, the request seems to work fine for few pages but is then erring out with :
could not initialize proxy - no Session
Method is as as below:
#Override
public Page<Person> findAllNotDeleted(final Pageable pageable)
{
final var criteria = createCriteria();
criteria.add(Restrictions.or(Restrictions.isNull(DELETED), Restrictions.eq(DELETED, false)));
criteria.setFetchMode(PERSON_RELATION, FetchMode.JOIN);
criteria.setFetchMode(DEPARTMENT_RELATION, FetchMode.JOIN);
criteria.setFirstResult((int) pageable.getOffset());
criteria.setMaxResults(pageable.getPageSize());
criteria.addOrder(asc("id"));
final var totalResult = getTotalResult();
return new PageImpl<>(criteria.list(), pageable, totalResult);
}
private int getTotalResult()
{
final Criteria countCriteria = createCriteria();
countCriteria.add(Restrictions.or(Restrictions.isNull(DELETED), Restrictions.eq(DELETED, false)));
return ((Number) countCriteria.setProjection(Projections.rowCount()).uniqueResult()).intValue();
}
Also, the call to findAllNotDeleted is done from a method anotated with #Transactional.
Not sure what is going wrong.
Any help would be highly appreciated.
EDIT
I read that FetchMode.Join does not work with Restrictions. So I tried implementing it using CriteriaBuilder but again stuck with the issue.
#Override
public Page<Driver> findAllNotDeleted(final Pageable pageable)
{
final var session = getCurrentSession();
final var builder = session.getCriteriaBuilder();
final var query = builder.createQuery(Person.class);
final var root = query.from(Driver.class);
root.join(PERSON_RELATION, JoinType.INNER)
.join(DEPARTMENT_RELATION,JoinType.INNER);
//flow does not reach here.....
var restrictions_1 = builder.isNull(root.get(DELETED));
var restrictions_2 = builder.equal(root.get(DELETED), false);
query.select(root).where(builder.or(restrictions_1,restrictions_2));
final var result = session.createQuery(query).getResultList();
return new PageImpl<>(result, pageable, result.size());
}
The flow does not seem to reach after root.join.
EDIT-2
The relations are as follows:
String PERSON_RELATIONSHIP = "person.address"
String DEPARTMENT_RELATION = "person.department"
and both person, address, department themselves are classes which extend Entity

Answer 1

I guess the associations you try to fetch i.e. PERSON_RELATION or DEPARTMENT_RELATION are collections? In such a case, it is not possible to directly do pagination on the entity level with Hibernate. You would have to fetch the ids first and then do a second query to fetch just the entities with the matching ids.
You could use Blaze-Persistence on top of Hibernate though which has a special pagination API that does these tricks for you behind the scenes. Here is the documentation about the pagination: https://persistence.blazebit.com/documentation/core/manual/en_US/index.html#pagination
There is also a Spring Data integration, so you could also use the Spring Data pagination convention along with Blaze-Persistence Entity-Views which are like Spring Data Projections on steroids. You'd use Page<DriverView> findByDeletedFalseOrDeletedNull(Pageable p) with
#EntityView(Driver.class)
interface DriverView {
Long getId();
String getName();
PersonView getPersonRelation();
DepartmentView getDepartmentRelation();
}
#EntityView(Person.class)
interface PersonView {
Long getId();
String getName();
}
#EntityView(Department.class)
interface DepartmentView {
Long getId();
String getName();
}
Using entity views will only fetch what you declare, nothing else. You could also use entity graphs though:
#EntityGraph(attributePaths = {"personRelation", "departmentRelation"})
Page<Driver> findByDeletedFalseOrDeletedNull(Pageable p);