JPA（三）之实体关系一对多（多对一）

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

1package com.sinoi.bean;
2
3import java.util.HashSet;
4import java.util.Set;
5
6import javax.persistence.CascadeType;
7import javax.persistence.Column;
8import javax.persistence.Entity;
9import javax.persistence.FetchType;
10import javax.persistence.GeneratedValue;
11import javax.persistence.Id;
12import javax.persistence.OneToMany;
13import javax.persistence.Table;
14
15@Entity
16@Table(name="my_order")
17public class Order {
18	@Id @Column(length=12)
19	private String orderId;
20	@Column(nullable=false)
21	private Float amount = 0f;
22	@OneToMany(cascade={CascadeType.REMOVE, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH},
23			mappedBy="order")
24	private Set<OrderItem> orderItems = new HashSet<OrderItem>();
25	public String getOrderId() {
26		return orderId;
27	}
28	public void setOrderId(String orderId) {
29		this.orderId = orderId;
30	}
31	public Float getAmount() {
32		return amount;
33	}
34	public void setAmount(Float amount) {
35		this.amount = amount;
36	}
37	
38	public Set<OrderItem> getOrderItems() {
39		return orderItems;
40	}
41	public void setOrderItems(Set<OrderItem> orderItems) {
42		this.orderItems = orderItems;
43	}
44	public void addOrderItem(OrderItem orderItem) {
45		orderItem.setOrder(this);//这句代码不加也可！
46		this.orderItems.add(orderItem);
47	}
48	
49	
50}

OrderItem.java代码

1package com.sinoi.bean;
2
3import javax.persistence.CascadeType;
4import javax.persistence.Column;
5import javax.persistence.Entity;
6import javax.persistence.GeneratedValue;
7import javax.persistence.Id;
8import javax.persistence.JoinColumn;
9import javax.persistence.ManyToOne;
10
11@Entity
12public class OrderItem {
13	@Id @GeneratedValue
14	private Integer id;
15	@Column(length=20, nullable=false)
16	private String productName;
17	@Column(nullable=false)
18	private Float sellPrice;
19	@ManyToOne(cascade={CascadeType.REFRESH, CascadeType.MERGE}, optional=false)
20	@JoinColumn(name="item_order_for")
21	private Order order;
22	public Order getOrder() {
23		return order;
24	}
25	public void setOrder(Order order) {
26		this.order = order;
27	}
28	public Integer getId() {
29		return id;
30	}
31	public void setId(Integer id) {
32		this.id = id;
33	}
34	public String getProductName() {
35		return productName;
36	}
37	public void setProductName(String productName) {
38		this.productName = productName;
39	}
40	public Float getSellPrice() {
41		return sellPrice;
42	}
43	public void setSellPrice(Float sellPrice) {
44		this.sellPrice = sellPrice;
45	}
46}

3.测试代码

1package junit.test;
2
3import javax.persistence.EntityManager;
4import javax.persistence.EntityManagerFactory;
5import javax.persistence.Persistence;
6
7import org.junit.Test;
8
9import com.sinoi.bean.Order;
10import com.sinoi.bean.OrderItem;
11
12public class UnitTest {
13	@Test
14	public void save() {
15		EntityManagerFactory entityManagerFactory = Persistence
16				.createEntityManagerFactory("unitname");
17		EntityManager entityManager = entityManagerFactory
18				.createEntityManager();
19		entityManager.getTransaction().begin();
20		
21		Order order = new Order();
22		order.setOrderId("jfdkf323");
23		order.setAmount(232f);
24		OrderItem orderItem = new OrderItem();
25		orderItem.setProductName("basketball");
26		orderItem.setSellPrice(221f);
27		OrderItem orderItem2 = new OrderItem();
28		orderItem2.setProductName("football");
29		orderItem2.setSellPrice(11f);
30		orderItem.setOrder(order);
31		orderItem2.setOrder(order);
32		order.addOrderItem(orderItem);
33		order.addOrderItem(orderItem2);
34
35		entityManager.persist(order);
36		entityManager.getTransaction().commit();
37		entityManager.close();
38		entityManagerFactory.close();
39		
40	}
41}

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