[FIXED] Map Flux into business DTO with list

Issue

I have the following entity:

public class EventCategoryEntity {

private UUID id;

@Column("category_name")
private String categoryName;

@Column("group_name")
private String groupName;

}

Which I retrieve via Flux(one to many relationship):

public Flux<EventCategoryEntity> findAllCategories() {
    return eventRepository.findAll();
}

@Query("select ec.id, ec.name as category_name,ecg.name as group_name" +
        "from event_category ec left join event_category_relation ecr on (ec.id = ecr.event_category_id) " +
        "left join event_category_group ecg on (ecr.event_category_group_id = ecg.id);")
Flux<EventCategoryEntity> findAll();

Then output via Controller in JSON response like:

    {
        "id": "87108493-4fc1-4b12-8ffc-e10aa039fc39",
        "categoryName": "soccer",
        "groupName": "team",
    },
    {
        "id": "87108493-4fc1-4b12-8ffc-e10aa039fc39",
        "categoryName": "soccer",
        "groupName": "ball",
    }
]

But I would like to aggregate response by id like this:

[
    {
        "id": "87108493-4fc1-4b12-8ffc-e10aa039fc39",
        "categoryName": "soccer",
        "groupName: ["team", "ball"]
    }
]

I've prepared DTO object, but I don't know how this flux map into the this:

public class EventCategory {
    private UUID id;

    private String categoryName;

    private List<CategoryGroup> categoryGroup;

    private class CategoryGroup {
        private String groupName;
    }
}

Solution

You can use collectMultimap which collects all elements emitted by this Flux into a Map.

@Test
public void collectMultimap() {

    Flux<EventCategoryEntity> flux1 = Flux.just(
            new EventCategoryEntity("87108493-4fc1-4b12-8ffc-e10aa039fc39","soccer","team"),
            new EventCategoryEntity("87108493-4fc1-4b12-8ffc-e10aa039fc39","soccer","ball"),
            new EventCategoryEntity("57108499-4fc1-4b52-8ffc-e11aa039fc85","soccer","tennis")
    );

    flux1.collectMultimap(EventCategoryEntity::getId, EventCategoryEntity::getGroupName)
            .map(ids -> ids.keySet().stream().map(t -> {
                 List<String> categoryGroupList =  ids.get(t).stream().toList();
                 Optional<EventCategoryEntity> f = flux1.toStream().filter(pp -> pp.getId().equals(t)).findFirst();

                return new EventCategoryDTO(f.get().getId(), f.get().getCategoryName(), categoryGroupList);
            }).toList())
            .subscribe(result -> System.out.println(result.toString()));
}

Output:

[EventCategoryDTO(id=87108493-4fc1-4b12-8ffc-e10aa039fc39, categoryName=soccer, categoryGroup=[team, ball]), EventCategoryDTO(id=57108499-4fc1-4b52-8ffc-e11aa039fc85, categoryName=soccer, categoryGroup=[tennis])]

https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Flux.html#collectMultimap-java.util.function.Function-java.util.function.Function-

Answered By - anicetkeric
Answer Checked By - Cary Denson (JavaFixing Admin)