1.背景介绍：

   对于购买商品时，订单信息（Order）和订单商品信息（OrderItem）的关系就是一对多的关系。

2.实体bean：

  Order.java代码

package com.sinoi.bean;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="my_order")
public class Order {
    @Id @Column(length=12)
    private String orderId;
    @Column(nullable=false)
    private Float amount = 0f;
    @OneToMany(cascade={CascadeType.REMOVE, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH},
            mappedBy="order")
    private Set<OrderItem> orderItems = new HashSet<OrderItem>();
    public String getOrderId() {
        return orderId;
    }
    public void setOrderId(String orderId) {
        this.orderId = orderId;
    }
    public Float getAmount() {
        return amount;
    }
    public void setAmount(Float amount) {
        this.amount = amount;
    }
    
    public Set<OrderItem> getOrderItems() {
        return orderItems;
    }
    public void setOrderItems(Set<OrderItem> orderItems) {
        this.orderItems = orderItems;
    }
    public void addOrderItem(OrderItem orderItem) {
        orderItem.setOrder(this);//这句代码不加也可！
        this.orderItems.add(orderItem);
    }
    
    
}

OrderItem.java代码

package com.sinoi.bean;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;

@Entity
public class OrderItem {
    @Id @GeneratedValue
    private Integer id;
    @Column(length=20, nullable=false)
    private String productName;
    @Column(nullable=false)
    private Float sellPrice;
    @ManyToOne(cascade={CascadeType.REFRESH, CascadeType.MERGE}, optional=false)
    @JoinColumn(name="item_order_for")
    private Order order;
    public Order getOrder() {
        return order;
    }
    public void setOrder(Order order) {
        this.order = order;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getProductName() {
        return productName;
    }
    public void setProductName(String productName) {
        this.productName = productName;
    }
    public Float getSellPrice() {
        return sellPrice;
    }
    public void setSellPrice(Float sellPrice) {
        this.sellPrice = sellPrice;
    }
}

3.测试代码

package junit.test;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

import org.junit.Test;

import com.sinoi.bean.Order;
import com.sinoi.bean.OrderItem;

public class UnitTest {
    @Test
    public void save() {
        EntityManagerFactory entityManagerFactory = Persistence
                .createEntityManagerFactory("unitname");
        EntityManager entityManager = entityManagerFactory
                .createEntityManager();
        entityManager.getTransaction().begin();
        
        Order order = new Order();
        order.setOrderId("jfdkf323");
        order.setAmount(232f);
        OrderItem orderItem = new OrderItem();
        orderItem.setProductName("basketball");
        orderItem.setSellPrice(221f);
        OrderItem orderItem2 = new OrderItem();
        orderItem2.setProductName("football");
        orderItem2.setSellPrice(11f);
        orderItem.setOrder(order);
        orderItem2.setOrder(order);
        order.addOrderItem(orderItem);
        order.addOrderItem(orderItem2);

        entityManager.persist(order);
        entityManager.getTransaction().commit();
        entityManager.close();
        entityManagerFactory.close();
        
    }
}

4.配置文件persistence.xml和前面JPA（一）、、、一样，在此省略