hibernate-pagination
Hibernate Pagination
Further reading:
Bootstrapping Hibernate 5 with Spring
A quick and practical guide to integrating Hibernate 5 with Spring.
Hibernate Inheritance Mapping
A practical guide to understanding different inheritance mapping strategies with JPA / Hibernate.
Show Hibernate/JPA SQL Statements from Spring Boot
Learn how you can configure logging of the generated SQL statements in your Spring Boot application.
2. Pagination with HQL and setFirstResult, setMaxResults API
Session session = sessionFactory.openSession();
Query query = sess.createQuery("From Foo");
query.setFirstResult(0);
query.setMaxResults(10);
List<Foo> fooList = fooList = query.list();
This example is using a basic Foo entity and is very much similar to the JPA with JQL implementation – the only difference being the query language.
If we turn on logging for Hibernate, we’ll see the following SQL being run:
Hibernate:
select
foo0_.id as id1_1_,
foo0_.name as name2_1_
from
Foo foo0_ limit ?
2.1. The Total Count and the Last Page
String countQ = "Select count (f.id) from Foo f";
Query countQuery = session.createQuery(countQ);
Long countResults = (Long) countQuery.uniqueResult();
And lastly, from the total number and a given page size, we can calculate the last page:
int pageSize = 10;
int lastPageNumber = (int) (Math.ceil(countResults / pageSize));
At this point we can look at a complete example for pagination, where we are calculating the last page and then retrieving it:
@Test
public void givenEntitiesExist_whenRetrievingLastPage_thenCorrectSize() {
int pageSize = 10;
String countQ = "Select count (f.id) from Foo f";
Query countQuery = session.createQuery(countQ);
Long countResults = (Long) countQuery.uniqueResult();
int lastPageNumber = (int) (Math.ceil(countResults / pageSize));
Query selectQuery = session.createQuery("From Foo");
selectQuery.setFirstResult((lastPageNumber - 1) * pageSize);
selectQuery.setMaxResults(pageSize);
List<Foo> lastPage = selectQuery.list();
assertThat(lastPage, hasSize(lessThan(pageSize + 1)));
}
3. Pagination with Hibernate Using HQL and the ScrollableResults API
Using ScrollableResults to implement pagination has the potential to reduce database calls. This approach streams the result set as the program scrolls through it, therefore eliminating the need to repeat the query to fill each page:
String hql = "FROM Foo f order by f.name";
Query query = session.createQuery(hql);
int pageSize = 10;
ScrollableResults resultScroll = query.scroll(ScrollMode.FORWARD_ONLY);
resultScroll.first();
resultScroll.scroll(0);
List<Foo> fooPage = Lists.newArrayList();
int i = 0;
while (pageSize > i++) {
fooPage.add((Foo) resultScroll.get(0));
if (!resultScroll.next())
break;
}
This method is not only time-efficient (only one database call), but it allows the user to get access to the total count of the result set without an additional query:
resultScroll.last();
int totalResults = resultScroll.getRowNumber() + 1;
On the other hand, keep in mind that, although scrolling is quite efficient, a large window may take up a decent amount of memory.
4. Pagination with Hibernate Using the Criteria API
Criteria criteria = session.createCriteria(Foo.class);
criteria.setFirstResult(0);
criteria.setMaxResults(pageSize);
List<Foo> firstPage = criteria.list();
Hibernate Criteria query API makes it very simple to also get the total count – by using a Projection object:
Criteria criteriaCount = session.createCriteria(Foo.class);
criteriaCount.setProjection(Projections.rowCount());
Long count = (Long) criteriaCount.uniqueResult();
As you can see, using this API will result in minimally more verbose code than plain HQL, but the API is fully type safe and a lot more flexible.
5. Conclusion
The implementation of this Spring JPA Tutorial can be found in the GitHub project – this is an Eclipse based project, so it should be easy to import and run as it is.