1.背景介紹：

?? 對于購買商品時，訂單信息（Order）和訂單商品信息（OrderItem）的關系就是一對多的關系。

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2.實體bean：

??Order.java代碼

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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);//這句代碼不加也可！ ????????this.orderItems.add(orderItem); ????} ????? ????? }

OrderItem.java代碼

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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; ????} }

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3.測試代碼

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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(); ????????? ????} }

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4.配置文件persistence.xml和前面JPA（一）、、、一樣，在此省略

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