How to limit the return results in a non-declarative query?

[Mpp1486356697]

I want to be the same “
Collection findByLastname(String lastname, Class type);
”
，But it failed.
public interface PersonDao extends JpaRepository<Person,Long>, JpaSpecificationExecutor
,QuerydslPredicateExecutor {

<C> Page<C> findAll(Specification<Person> spec, Pageable pageable,Class<C> c);
<C> Page<C>  findAll(Predicate predicate, Pageable pageable,Class<C> c);

}
Using Querydsl to construct conditions is very convenient, but it does not allow limiting the return results - I don't want to use it “new JPAQueryFactory(em).select(QPerson.person.name).where(....,

[mp911de]

Have you seen the findBy method that allows limiting?

List<User> results = repo.findBy(predicate, query -> query.limit(10).all());

Generally, Pageable allows limit results to one page if you're looking for a simpler API.

[Mpp1486356697]

Have you seen the findBy method that allows limiting?

List<User> results = repo.findBy(predicate, query -> query.limit(10).all());

Generally, Pageable allows limit results to one page if you're looking for a simpler API.

Yes, you are correct.
Why doesn't findBy behave like findAllByName? “select p1_0.name ”
But instead "p1_0.id,p1_0.age,p1_0.name,p1_0.phone_id "
Or rather, what should I do then?

 personDao.findBy(Example.of(new Person("lrb",null,null)),
x -> x.as(PersonOnlyName.class).page(PageRequest.of(1, 1)));
// Hibernate: select p1_0.id,p1_0.age,p1_0.name,p1_0.phone_id from person p1_0 where p1_0.name=? limit ?,?
// Hibernate: select p1_0.id,p1_0.name from phone p1_0 where p1_0.id=?
// Hibernate: select count(p1_0.id) from person p1_0 where p1_0.name=?
personDao.findBy(Example.of(new Person("lrb",null,null)),
x -> x.project("name").page(PageRequest.of(1, 1)));
// Hibernate: select p1_0.id,p1_0.age,p1_0.name,p1_0.phone_id from person p1_0 where p1_0.name=? limit ?,?
// Hibernate: select count(p1_0.id) from person p1_0 where p1_0.name=?
Page lrb = personDao.findAllByName("lrb", PageRequest.of(1, 1), PersonOnlyName.class);
// Hibernate: select p1_0.name from person p1_0 where p1_0.name=? limit ?,?
// Hibernate: select count(p1_0.id) from person p1_0 where p1_0.name=?

[mp911de]

findBy projections use fetch graphs instead of tuple queries. I think that is something we can improve on, see also #2600.