How to map Iterable to its DTO?

Question

I have the following repository:

PermissionRepository:

public interface PermissionRepository extends CrudRepository<Permission, Long>,
        SearchRepository<Permission> {

}

In my service, I am trying to map Permission entity to PermissionDTO, but as findAll() method returns Iterable<T> (Iterable<T> findAll();), I cannot convert as shown below as I generally use for List<T>. It throws "Cannot resolve method 'stream' in 'Iterable'" error for the .stream() method.

List<PermissionDTO> list = permissionRepository.findAll()
        .stream()
        .map(PermissionDTO::new)
        .collect(Collectors.toList());

So, how can I map this Permission entity to PermissionDTO?

I guess you are using Spring Data? How about using `JpaRepository` instead of `CrudRepository`. `findAll` of `JpaRepository` returns a `List`, — magicmn, Oct 25 '21 at 08:33
[Convert Iterable to Stream using Java 8 JDK](https://stackoverflow.com/questions/23932061/convert-iterable-to-stream-using-java-8-jdk) -> that's probably what you're looking for. — ernest_k, Oct 25 '21 at 08:34
@RobbyCornelissen It throws "*Cannot resolve method 'stream' in 'Iterable'*" error for the `.stream()` method. — , Oct 25 '21 at 08:38
@magicmn Yes, it seems possible but at first I do not want to change that part if there is another smart solution for this. — , Oct 25 '21 at 08:43
Does this answer your question? [Convert Iterable to Stream using Java 8 JDK](https://stackoverflow.com/questions/23932061/convert-iterable-to-stream-using-java-8-jdk) — Maurice Perry, Oct 25 '21 at 08:47
@MauricePerry I tried to use it, but cannot. How should I apply that approach to my code above? — , Oct 25 '21 at 08:51

score 0 · Accepted Answer · answered Oct 25 '21 at 08:50

0

There are 3 ways to do what you want

Override findAll and make it return a List

public interface PermissionRepository extends CrudRepository<Permission, Long> {
    @Override
    List<Permission> findAll();
}

Implement JpaRepository instead of CrudRepository.

public interface PermissionRepository extends JpaRepository<Permission, Long>,
    SearchRepository<Permission>

Convert Iterable to Stream using StreamSupport.

StreamSupport.stream(iterable.spliterator(), false).map(PermissionDTO::new)
    .collect(Collectors.toList());

answered Oct 25 '21 at 08:50

magicmn

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15

Perfect explanations and good answer. I think it will fix the problem, but in all of these approaches, I get a warning "*Required type: Function, Provided: *". What is the mistake? – Oct 25 '21 at 08:58
Hm a random guess is that `PermissionDTO::new` is not working as expected. Your PermissionDTO has a PermissionDTO(Permission) constructor right? – magicmn Oct 25 '21 at 09:03
Is there any problem with `.map(PermissionDTO::new)` line? – Oct 25 '21 at 09:04
1

I think so `.map(PermissionDTO::new)` is a shortcut for `.map(permission -> new PermissionDTO(permission))`. Is that working? – magicmn Oct 25 '21 at 09:05
Adding the necessary constructor fixed the problem, thanks a lot. – Oct 25 '21 at 09:07

How to map Iterable to its DTO?

1 Answers1