Deleting in relationships in Java SpringBoot

Good Day developers , i'm hardly striving with this problem on my App which use SpringBoot framework.Basically can't put two and two together about how deleting one of the items in the relation ship once its parent is delete. Here my explanation:
First both entities with its respective relation to each other:

Product(Children)

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO,generator = "native")
    @GenericGenerator(name="native",strategy="native")
    private Long id;

    @OneToMany(mappedBy = "products",fetch= FetchType.EAGER,cascade = CascadeType.ALL, orphanRemoval = true)
    private Set<Category> categorySet= new HashSet<>();

    CONSTRUCTOR FOR PRODUCTS ENTITY 
-------------------------------------GETTERS AND SETTERS---------------------------------
 

Being this the Product entity under the premise of one product being able to clasify to several categories hence its relation OnetoMany.Then:

Categories(Parent)

@Entity
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO,generator = "native")
    @GenericGenerator(name="native",strategy="native")
    private Long id;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name="product_id")
    private Product products;

    CONSTRUCTOR FOR CATEGORY ENTITY 

     ---------------------------GETTERS AND SETTERS-----------------------------

Following the former concept but withan inverse logic applied Category reltion toward products, and works perect on my database.
on repositories lets say i set this

Category Repository

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.CrudRepository;
import org.springframework.data.rest.core.annotation.RepositoryRestResource;
import java.util.Collection;

@RepositoryRestResource
public interface CategoryRepository extends JpaRepository <Category,Long> {
}

Product Repository

package com.miniAmazon;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.*;
import org.springframework.data.repository.CrudRepository;
import org.springframework.data.rest.core.annotation.RepositoryRestResource;

@RepositoryRestResource
public interface ProductRepository extends CrudRepository<Product,Long> {
    Product findByProductName (String productName);
}

Then trying to set the command to delete products or categories from my Jpa and Crud Reps, using Junit Test on the Category Entity, like this:

Category Entity

 @Test
    public static void whenDeletingCategories_thenProductsShouldAlsoBeDeleted() {
        ProductRepository.deleteAll();
        assert(CategoryRepository.count()).isEqualTo(0);
        assert(ProductRepository.count()).isEqualTo(0);
    }

@Test
    public static void whenDeletingProducts_thenCategoriesShouldAlsoBeDeleted() {
        CategoryRepository.deleteAll();
        assert(CategoryRepository.count()).isEqualTo(0);
        assert(ProductRepository.count()).isEqualTo(2);
    }

Throws me an error saying that "Non-static method 'deleteAll()/count()' cannot be referenced from a static context".
Any idea about why this is happening .Any advice ?.Thanks in advance!!!!.Have a good day!!!

You are try to use Non-static method of interface but deleteAll() or count() are not static method. Try to create a repository object then autowired it to call deleteAll() / count() method.

@Autowired
private CategoryRepository categoryRepository;

And use categoryRepository to call call deleteAll() / count() method

categoryRepository.deleteAll();
assert(categoryRepository.count()).isEqualTo(0);

Try using instantiated beans CategoryRepository and ProductRepository instead of the interfaces.