I have a simple form that intend to update a list of items in a cart. The form works pretty well, I display an input text for each item in the cart. But if I change an item text and then save, it fails with an hibernate error : PersistenceException occured : org.hibernate.PersistentObjectException: detached entity passed to persist: models.Item

此处为:

<section class="form">
    #{form @save()}
        <input type="hidden" name="cart.id" value="${cart?.id}">

        <p class="field">
            <label for="title">Title :</label>
            <input type="text" name="cart.title" value="${cart?.title}"
            maxlength="50" size="50"/>
            <span class="error">${errors.forKey( cart.title )}</span>
        </p>

        <div id="items">
            #{if cart && cart.items}
                            #{list items:cart.items, as: item }
                                    <input type="hidden" name="cart.items[${item_index}].id" value="${item?.id}">
                                    <input type="text"    name="cart.items[${item_index}].text" value="$
{item?.text}"/>
                        #{/list}
                    #{/if}
        </div>

        <p class="buttons">
            <a href="@{index()}">Cancel</a> <input type="submit" value="Save" id="savecart">
        </p>
    #{/form}
</section>

我的实体和控制人:

@Entity
public class Cart extends Model {
    @Required
    public String title;

    @OneToMany(mappedBy = "cart", cascade = CascadeType.ALL)
    public List<Item> items;

    public Cart(String title) {
            this.title = title;
            this.items = new ArrayList<Item>();
    }
}


@Entity
public class Item extends Model {
    @Required
    public String text;

    @ManyToOne
    @Required
    public Cart cart;

    public Item(String text, Cart cart) {
            this.text = text;
            this.cart = cart;
    }

}

public static void save(Cart cart){
    validation.valid(cart);
            if (validation.hasErrors()) {
                    validation.keep();
                    formCart(cart.id);
            }
            cart.save();
            index();
} 

I think it s a common use case, however I m not sure to do it the right way.