假设我有两个模型：

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Category {
  @Id
  @GeneratedValue
  private Long id;
  
  @Basic(optional = false)
  private String name;
  
  @ManyToMany(mappedBy = "categories", cascade = { CascadeType.MERGE, CascadeType.PERSIST })
  private List<Product> products;
}

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Product {
  
  @Id
  @GeneratedValue
  private Long id;
  
  @ManyToMany(cascade = { CascadeType.MERGE, CascadeType.PERSIST})
  private List<Category> categories;
}

当我试图持久化一个产品，里面有一些类别，就像这样：

@Bean
CommandLineRunner t(CategoryRepository categoryRepository, ProductRepository productRepository) {
    return new CommandLineRunner() {
        @Override
        @Transactional
        public void run(String... args) throws Exception {
            categoryRepository.save(new Category(null, "name 1", null));
            categoryRepository.save(new Category(null, "name 2", null));
            categoryRepository.save(new Category(null, "name 3", null));

            List<Category> all = categoryRepository.findAll();
            all.add(new Category(null, "$$$", null));

            productRepository.save(new Product(null, all));
            
        }
    };
}

它确实工作，我可以看到“连接表”x1c 0d1x中的数据
但是如果我还原这个过程，persist a category with some products inside的意思是：

@Bean
CommandLineRunner t(CategoryRepository categoryRepository, ProductRepository productRepository) {
    return new CommandLineRunner() {
        @Override
        @Transactional
        public void run(String... args) throws Exception {
            productRepository.save(new Product());
            productRepository.save(new Product());
            productRepository.save(new Product());

            List<Product> all = productRepository.findAll();
            all.add(new Product());

            categoryRepository.save(new Category(null, "%%%%%%%%", all));
        }
    };
}

虽然它没有抛出任何错误/异常，但结果并不是我所期望的。我认为它应该像第一种情况--“连接表”应该有一些行--但实际上只有category和product包含行。
你能解释一下为什么第二个案子不行吗？是虫子吗？