java - Spring MVC OneToMany，在镜头中从父母保存到孩子

Question

订单.java

@Entity
@Table(name = "orders") 
public class Order {
     @Id
     @GeneratedValue(strategy=GenerationType.IDENTITY)
     @Column(name = "id")
     private int id;

     @Column(name = "created_at")
     private Date createdAt;

     @OneToMany
     private List<Product> orderItem;


    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Date getCreatedAt() {
        return createdAt;
    }

    public void setCreatedAt(Date createdAt) {
        this.createdAt = createdAt;
    }

    public List<Product> getOrderItem() {
        return orderItem;
    }

    public void setOrderItem(List<Product> orderItem) {
        this.orderItem = orderItem;
    }

订单产品.java

@Entity
@Table(name = "orders_product")
public class OrderProduct {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name = "id")
    private int id;

    @Column(name = "order_id")
    private int orderId;
    @Column(name = "orderItem_id")
    private int orderItemId;

    @Column(name = "quantity")
    private int quantity;

    public int getQuantity() {
        return quantity;
    }
    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
    public int getOrderId() {
        return orderId;
    }
    public void setOrderId(int orderId) {
        this.orderId = orderId;
    }
    public int getOrderItemId() {
        return orderItemId;
    }
    public void setOrderItemId(int orderItemId) {
        this.orderItemId = orderItemId;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }

产品.java

@Entity
@Table(name = "product")
public class Product {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id")
    private int id;

    @Column(name="code")
    private String code;

    @Column(name="name")
    private String name;

    @Column(name="price")
    private double price;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Product [id=" + id + ", code=" + code + ", name=" + name + ", price=" + price + "]";
    }


}

我尝试从订单中保存并设置orderItem，并且只有已插入表格的订单ID和产品ID，我也尝试插入数量，但不知道该怎么做。