Olá, boa tarde.

Estou tendo o seguinte erro na hora de executar o código:

Row was already updated or deleted by another transaction for entity [br.com.pedropgaraujo.purchasemanager.model.Category with id '3']

Irei deixar abaixo minha classe category e a principal onde está sendo executado o código.

Category.class

package br.com.pedropgaraujo.purchasemanager.model;

import jakarta.persistence.*;

import java.util.ArrayList;
import java.util.List;

@Entity
public class Category {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    @OneToMany(mappedBy = "category", cascade = CascadeType.ALL)
    private List<Product> productList = new ArrayList<>();

    public Category(){}

    public Category(Long id, String name) {
        this.id = id;
        this.name = name;
    }

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public List<Product> getProductList() {
        return productList;
    }

    public void setProductList(List<Product> productList) {
        this.productList = productList;
    }
}

Principal.class

package br.com.pedropgaraujo.purchasemanager;

import java.time.LocalDate;
import java.util.List;

@Component
public class Principal {

    @Autowired
    private ProductRepository productRepository;
    @Autowired
    private CategoryRepository categoryRepository;
    @Autowired
    private ClientOrderRepository clientOrderRepository;
    @Autowired
    private SupplierRepository supplierRepository;

    public Principal (ProductRepository productRepository, CategoryRepository categoryRepository, ClientOrderRepository clientOrderRepository){
        this.categoryRepository = categoryRepository;
        this.productRepository = productRepository;
        this.clientOrderRepository = clientOrderRepository;
    }
Category categoryFurniture = new Category(1L, "Furniture");
    Category categoryBooks = new Category(2L, "Books");
    Category categoryEletronics = new Category(3L, "Eletronics");

    Product product1 = new Product("Notebook",5000.0, categoryEletronics);
    Product product2 = new Product("Smartphone", 2500.0, categoryEletronics);
    Product product3 = new Product("Livro Java", 150.0, categoryBooks);
    Product product4 = new Product("Livro Spring Boot", 100.0, categoryBooks);

    Supplier supplierTech = new Supplier("Tech Supplier");
    Supplier supplierBook = new Supplier("Global Library");

    ClientOrder clientOrder1 = new ClientOrder(1L, LocalDate.now());
    ClientOrder clientOrder2 = new ClientOrder(2L, LocalDate.now().minusDays(1));

    public void principalTwo(){
        //Creating category on DB
        categoryRepository.saveAll(List.of(categoryEletronics,categoryBooks,categoryFurniture));

        //Creating suppliers on DB
        supplierRepository.saveAll(List.of(supplierTech, supplierBook));

        //Creating products on DB
        product1.setSupplier(supplierTech);
        product2.setSupplier(supplierTech);
        product3.setSupplier(supplierBook);
        product4.setSupplier(supplierBook);
        productRepository.saveAll(List.of(product1, product2, product3, product4));

        //Creating Orders
        clientOrder1.setProductList(List.of(product1, product3));
        clientOrder2.setProductList(List.of(product2, product4));


        //Testing consults and verify relationship
        System.out.println("Products on category Eletronics: ");
        categoryRepository.findById(1L).ifPresent(c ->
                        c.getProductList().forEach(p ->
                                System.out.println(" - " + p.getName())
                        )
        );


        System.out.println("\nOrder and products: ");
        clientOrderRepository.findAll().forEach(o -> {
            System.out.println("Order " + o.getId() + ":");
            o.getProductList().forEach(p ->
                    System.out.println(" - " + p.getName()));
        });


        System.out.println("\nProducts and suppliers: ");
        productRepository.findAll()
                .forEach(p ->
                        System.out.println(
                                "Product: " + p.getName() +
                                ", Supplier: " + p.getSupplier().getName()));
    }

}

Retirei alguns imports deste código postado aqui, somente porque atingiu o limite máximo de caracteres.