1、persistence.xml檔案

</pre><pre name="code" class="html">資料庫使用oracle

<?xml version="1.0" encoding="UTF-8"?>  
<persistence xmlns="http://java.sun.com/xml/ns/persistence" 
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xsi:schemaLocation="http://java.sun.com/xml/ns/persistence 
 http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" 
 version="1.0"> 

 <persistence-unit name="jpa" transaction-type="RESOURCE_LOCAL"> 
	 <properties> 
	 	<property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect" /> 
	
	 	<property name="hibernate.connection.driver_class" value="oracle.jdbc.driver.OracleDriver" /> 
	 	<property name="hibernate.connection.username" value=" " /> 
	 	<property name="hibernate.connection.password" value=" " /> 
	 	<property name="hibernate.connection.url" value="jdbc:oracle:thin:@xxx.xxx.xxx.xxx:1521:xxxx" /> 
	 	<property name="hibernate.max_fetch_depth" value="5" /> 
	 	<property name="hibernate.jdbc.fetch_size" value="20" /> 
	 	<property name="hibernate.jdbc.batch_size" value="10" /> 
	
	 	<property name="hibernate.hbm2ddl.auto" value="update" /> 
	 	<property name="hibernate.show_sql" value="true" /> 
	 	<property name="hibernate.format_sql" value="false" /> 
	 </properties> 
 </persistence-unit> 
</persistence>
 

2、訂單類

package entity.oneToMany;

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

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

import org.hibernate.annotations.GenericGenerator;
@Entity
@Table(name="myorders")
public class Order {
	
	private Integer id;
	private String orderId;
	private Float total;
	
	private Set<OrderItem> items=new HashSet<OrderItem>();
	
	
	
	@Id @GeneratedValue
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getOrderId() {
		return orderId;
	}
	public void setOrderId(String orderId) {
		this.orderId = orderId;
	}
	@Column(nullable=false)
	public Float getTotal() {
		return total;
	}
	public void setTotal(Float total) {
		this.total = total;
	}
	//關係被維護端
	@OneToMany(cascade=CascadeType.ALL,mappedBy="order")
	public Set<OrderItem> getItems() {
		return items;
	}
	public void setItems(Set<OrderItem> items) {
		this.items = items;
	}
	
	/*public void add(OrderItem o){
		this.items.add(o);
	}*/
}
 

package entity.oneToMany;

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;
import javax.persistence.Table;

@Entity
@Table(name="myorderItem")
public class OrderItem {
	
	private Integer id;
	private String productName;
	private Float sellPrice;
	
	private Order order;
	
	@Id @GeneratedValue
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	@Column(nullable=false)
	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;
	}
	//關係維護端  設定外來鍵
	@ManyToOne(cascade={CascadeType.REFRESH,CascadeType.MERGE},optional=false)
	@JoinColumn(name="order_id")
	public Order getOrder() {
		return order;
	}
	public void setOrder(Order order) {
		this.order = order;
	}
	
}
 

<span style="white-space:pre">	</span>@Test
	public void save(){
		EntityManagerFactory factory = Persistence.createEntityManagerFactory("jpa");
		EntityManager em = factory.createEntityManager();
		//System.out.println(em);
		EntityTransaction transaction = em.getTransaction();
		transaction.begin();
		
		Order order = new Order();
		
		OrderItem orderItem1 = new OrderItem();
		orderItem1.setProductName("羽毛球");
		orderItem1.setSellPrice(45f);
		orderItem1.setOrder(order);
		
		OrderItem orderItem2 = new OrderItem();
		orderItem2.setProductName("籃球球");
		orderItem2.setSellPrice(95f);
		orderItem2.setOrder(order);
		
		Set<OrderItem> items=new HashSet<OrderItem>();
		items.add(orderItem2);
		items.add(orderItem1);
		
		order.setOrderId("20151201123");
		order.setTotal(100f);
		order.setItems(items);
		
		em.persist(order);
		
		transaction.commit();
		em.close();
		factory.close();
		//System.out.println(factory);
	}

總結：

1、在處理一對多關係時，通常都是"多"的一方作為關係維護端,"一"的一方為關係被維護端；（黎活明老師提的觀點）

2、最重要的註解如何寫呢？

完成以下幾件事即可：

a.關係維護端（即多的一方）在關聯屬性的get方法上加@ManyToOne註解，並設定cascade級聯、optional=false；

如：@ManyToOne(cascade={CascadeType.REFRESH,CascadeType.MERGE},optional=false)

b.關係維護端（即多的一方）在關聯屬性的get方法上加@JoinColumn註解，並設定外來鍵名稱，

如@JoinColumn(name="order_id")

c.關係被維護端（即“一”的一方），在關聯的屬性的get方法上加@OneToMany註解，並設定cascade級聯、mappedBy屬性（多的一方的那個欄位名）

如：@OneToMany(cascade=CascadeType.ALL,mappedBy="order")

3.完了，上面的第二點是處理對映關係中的重要內容。

希望可以幫到你，謝謝！