JPA Specifications - dealing with optional parameters

[must Janik]

I tried to create dynamic query using JPA specification, but I'm not sure whether I understood the JPA specification properly. I was using https://www.baeldung.com/spring-data-criteria-queries to write the code. The case is, I got some paramters that are optionals, so first I've written all

CriteriaBuilder, CriteriaQuery

etc alone. like this (from above site):

CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<Book> cq = cb.createQuery(Book.class);
 
    Root<Book> book = cq.from(Book.class);
    List<Predicate> predicates = new ArrayList<>();
    
    if (authorName != null) {
        predicates.add(cb.equal(book.get("author"), authorName));
    }
    if (title != null) {
        predicates.add(cb.like(book.get("title"), "%" + title + "%"));
    }
    cq.where(predicates.toArray(new Predicate[0]));
 
    return em.createQuery(cq).getResultList();

while scrolling down the site I could read about JPA specifiaction and it looked much more better, because within each parameters I got next if using above solution.

Using JPA specification the code looks like this for now:

fun getAdvertisementsBasedOnParameters(searchInput: String?, city: String?, category: AdvertisementCategory?): List<AdvertisementSearchResult> {
        val advertisements: MutableList<AdvertisementEntity> = advertisementRepository
                .findAll(where(hasCategory(category))
                        ?.and(hasCity(city)
                                ?.and(titleContains(searchInput))))

        return advertisements.map {
            AdvertisementSearchResult(
                    it.id,
                    it.imageUrl,
                    it.title
            )
        }
    }

fun hasCity(city: String?): Specification<AdvertisementEntity?>? {
        return Specification { book: Root<AdvertisementEntity?>,
                               _: CriteriaQuery<*>?,
                               cb: CriteriaBuilder ->
            cb.equal(book.get<Any>("city"), city)
        }
    }

    fun hasCategory(category: AdvertisementCategory?): Specification<AdvertisementEntity?>? {
        return Specification { book: Root<AdvertisementEntity?>,
                               _: CriteriaQuery<*>?,
                               cb: CriteriaBuilder ->
            cb.equal(book.get<Any>("category"), category)
        }
    }

    fun titleContains(title: String?): Specification<AdvertisementEntity?>? {
        return Specification { advertisement: Root<AdvertisementEntity?>,
                               _: CriteriaQuery<*>?,
                               cb: CriteriaBuilder ->
            cb.like(advertisement.get("title"), "%$title%")
        }
    }

As you can see code looks much more better, I got rid of boiler plate, but the problem is, just those advertisements are returned that meet all requirements so it has category/city/proper title.

If I got

advertisementRepository.save(
                AdvertisementEntity(
                        title = "Some random title :)",
                        imageUrl = "", //TODO add some imageUrl
                        city = "Warsaw",
                        dateOfCreation = LocalDateTime.now(),
                        description = "Some random description, Some random description, Some random description, " +
                                "Some random description, Some random description, Some random description ",
                        category = AdvertisementCategory.MUSIC,
                        createdByUserID = id
                )
        )

and if I put only Warsaw I want it to be returned, if I put only random (as title) I want it to be returned etc etc, for now if I put Warsaw, random (as title), MUSIC Could you tell me how to do it?


PS: The code  I write is kotlin, but it is very similiar to java so you can propose solution in java if you want.
Thanks a lot for help!

//edit

I changed to

   

var advertisements: MutableList<AdvertisementEntity> = advertisementRepository
                    .findAll(where(hasCategory(category))
                            ?.or(hasCity(city)
                                    ?.or(titleContains(searchInput))))

and it works, but the question is, how to make to return all the advertisements if no parameters where passed.