我如何使用 Spring 注释将 map cart-cartItem-item 实体与 JPA 结合使用？

Question

I'm a beginner at JPA and table relationships and I've watched a few tutorials and consider the below to be correct(?). But I'd appreciate if a more experienced eye took a look at the below if it seems right.

I have a Cart, CartItem and an Item class. A Cart can have many CartItems. A CartItem can have one Item and also is part of one Cart. An Item can be in many CartItems.

I'm trying to get the relationship between the tables right but I would appreciate some help since it doesn't seem to work. I'm getting an error Cannot invoke "java.util.List.iterator()" because the return value of "...Cart.getItems()" is null. I'm assuming it's because I've set up the relationship of my tables incorrectly?

Cart:

@Entity
@Table(name="my_cart")
public class Cart {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="cart_id")
    private String cartId;

    @OneToMany(targetEntity = CartItem.class, cascade = CascadeType.ALL)
    @JoinColumn(name="cart_item_foreign_key")
    @Column(name="cart_items")
    private List<CartItem> cartItems;

    @Column(name="cart_total_number_of_items")
    private long totalNumberOfItems;
    @Column(name="cart_total_price")
    private double totalPrice;

// + getters and setters and constructor

CartItem:

@Entity
@Table(name="cart_items")
public class CartItem {
    @Id
    @Column(name="cartitem_id")
    private String itemId;
    @Column(name="cart_item_name")
    private String productName;
    @Column(name="cart_item_description")
    private String itemDescription;
    @Column(name="cart_item_quantity")
    private int itemQuantity;
    @Column(name="cart_item_price")
    private double itemPrice;

    @ManyToOne
    Cart cart;

    @OneToOne
    private Item product;

Item:

@Entity
@Table(name="my_items")
public class Item {
    @Id
    @Column(name="item_id")
    private String itemId;
    @Column(name="item_name", nullable = false)
    private String name;
    @Column(name="item_description", nullable = false)
    private String description;
    @Column(name="item_price", nullable = false)
    private Double price;

    @OneToOne(mappedBy = "item")
    CartItem cartItem;

Could someone with more experience please point me in the right direction with the above table relationships? Thank you

Answer 1

In the Cart class, when you use @JoinColumn , you can omit @Column , in @JoinColumn there is a name attribute that is the column name.