Identifier does not correctly propagate from root to child aggregate on insert

[mipo256]

I've created the sample repo to demonstrate the problem. Run the following test:

In a nutshell, assume we have an aggregate:

@Table
public class Category {

  @Id
  private Long id;

  private String name;

  @MappedCollection(idColumn = "category_id", keyColumn = "category_id")
  private List<ProductCategories> productCategories;
}

@Table
public class Product implements Persistable<Long> {

  @Id
  private Long id;

  private String name;

  @MappedCollection(keyColumn = "product_id", idColumn = "product_id")
  private List<ProductCategories> productCategories;
}

@Table
public class ProductCategories {

  private AggregateReference<Product, Long> productId;
  private AggregateReference<Category, Long> categoryId;
}

And when running the following code, the loaded foundProcdut does not contain the ProductCategories:

Product product = Product.createNew(
    1L,
    "product first",
    List.of(
        new ProductCategories()
            .setProductId(AggregateReference.to(1L))
            .setCategoryId(AggregateReference.to(1L))
    )
);

// when.
Product saved = productRepository.save(product);

// then.
Optional<Product> foundProduct = productRepository.findById(saved.getId());

The reason it does not contain ProductCategories is because the INSERT, generated into ProductCategories, has product_id set to 0, instead of 1.

Note: It does not even matter is the ID generated on the client side or as an IDENTITY column on the database side. The problem remains.