替换双向一对多关系中的集合

Question

Given the following JPA entities that have a bidirectional one-to-many relationship

@Entity
public class Cart {

    @OneToMany(mappedBy="cart")
    private Set<Items> items;
    
    // getters and setters
}

@Entity
public class Items {
    
    @ManyToOne
    @JoinColumn(name="cart_id", nullable=false)
    private Cart cart;
    
    // getters and setters
}

If I load a cart from the database that already contains some items

Cart cartWithItems = CartRepository.findById(cartId);

And I want to replace the items in this cart with a new collection of items

Set<Item> newCartItems = ItemRepository.findAllById(newItemIds);

What is the simplest/best way to perform this replacement? Ideally, I would like the generated SQL statements to be reasonably efficient, but my main goal is perform the replacement using code that's concise and readable.

Update

Just to be clear about what I mean by replacement:

If the cart initially contains items with IDs 2, 3, 4 and newItemIds contains 4, 5, 6, then after the replacement, the cart should contain items with IDs 4, 5, 6, and items with IDs 2, 3 should continue to exist (ie they should not be deleted).

Answer 1

I'd recommend adding orphanRemoval = true to your OneToMany annotation and then just remove the items from your cart. Furthermore I would recommend an add method that handles the bidirectional part like this:

public void addItem(Item item) {
  if(item != null) {
    this.items.add(item);
    item.setCart(this);
  }
}

You could also add a remove function if you wanted to. The addItem function could be used like this:

cartWithItems.setItems(new HashSet<>());
newCartItems.forEach(cartWithItems::addItem);

Hope this answers your question.