Hibernate 使用 Annotation 之 ManyToOne(单向关联关系)

Java代码如下：

package com.lwp.hibernate.Model;

import java.io.Serializable;

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

@Entity
@Table
public class Customer implements Serializable{
	
	private static final long serialVersionUID = 1L;

	public Customer(){}
	public Customer(String name){
		this.name=name;
	}
	@Id
	@GeneratedValue
	@Column(name="ID")
	private Long id;
	
	@Column(name="NAME",length=15)
	private String name;

	public Long getId() {
		return id;
	}

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

	public String getName() {
		return name;
	}

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

package com.lwp.hibernate.Model;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="ORDERS")
public class Order implements Serializable{

	private static final long serialVersionUID = 1L;
	public Order(){}

	public Order(String orderNumber,Customer customer){
		this.orderNumber =orderNumber;
		this.customer=customer;
	}
	@Id
	@GeneratedValue
	@Column(name="ID")
	private Long id;
	
	@Column(name="ORDER_NUMBER",length=15)
	private String orderNumber;
	
	@ManyToOne(fetch = FetchType.EAGER)
	@JoinColumn(name="CUSTOMER_ID", nullable = false)
	private Customer customer;

	public Long getId() {
		return id;
	}

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

	public String getOrderNumber() {
		return orderNumber;
	}

	public void setOrderNumber(String orderNumber) {
		this.orderNumber = orderNumber;
	}

	public Customer getCustomer() {
		return customer;
	}

	public void setCustomer(Customer customer) {
		this.customer = customer;
	}
}

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;

import com.lwp.hibernate.Model.Customer;
import com.lwp.hibernate.Model.Order;


public class CustomerTest {

    public static void main(String[] args) {
        new SchemaExport(new AnnotationConfiguration().configure("/hibernate.cfg.xml")).create(true, false);
        Customer customer = new Customer("Tom");
        Order order1 = new Order("Tom_Order001",customer);
        Order order2 = new Order("Tom_Order002",customer);
        save(customer);
        save(order1);
        save(order2);
    }

    public static void save(Object o){
        //Configuration cfg = new Configuration();//xx.hbm.xml形式下的new  
        Configuration cfg = new AnnotationConfiguration(); //Annotation形式下的new
        SessionFactory sf = cfg.configure().buildSessionFactory();
        Session session = sf.openSession();
        session.beginTransaction();
        session.save(o);
        session.getTransaction().commit();
        session.close();
        sf.close();
    }
}

hibernate.cfg.xml:

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <!-- Database connection settings -->
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
        <property name="connection.username">root</property>
        <property name="connection.password">root</property>

        <!-- JDBC connection pool (use the built-in) -->
        <!-- <property name="connection.pool_size">1</property> -->

        <!-- SQL dialect 方言-->
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

        <!-- Enable Hibernate's automatic session context management -->
        <!--<property name="current_session_context_class">thread</property> -->

        <!-- Disable the second-level cache  -->
        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>

        <!-- Echo all executed SQL to stdout 打印sql语句 -->
        <property name="show_sql">true</property>

        <!-- Drop and re-create the database schema on startup 让hibernate自动生成建表语句 -->
        <!-- validate   加载hibernate时，验证创建数据库表结构
			create      每次加载hibernate，重新创建数据库表结构，这就是导致数据库表数据丢失的原因。
			create-drop 加载hibernate时创建，退出是删除表结构
			update      加载hibernate自动更新数据库结构 -->
         <property name="hbm2ddl.auto">update</property>

       
        <!-- xx.hbm.xml形式
        	<mapping resource="com/lwp/hibernate/Model/Customer.hbm.xml"/>
         	 <mapping resource="com/lwp/hibernate/Model/Order.hbm.xml"/>
        --> 
        <!-- Annotation形式 -->
       		 <mapping class="com.lwp.hibernate.Model.Customer"/>
          	 <mapping class="com.lwp.hibernate.Model.Order"/>  
    </session-factory>

</hibernate-configuration>

SQL：

alter table ORDERS drop foreign key FK8B7256E5C1E4F651
drop table if exists Customer
drop table if exists ORDERS
create table Customer (ID bigint not null auto_increment, NAME varchar(15), primary key (ID))
create table ORDERS (ID bigint not null auto_increment, ORDER_NUMBER varchar(15), CUSTOMER_ID bigint not null, primary key (ID))
alter table ORDERS add index FK8B7256E5C1E4F651 (CUSTOMER_ID), add constraint FK8B7256E5C1E4F651 foreign key (CUSTOMER_ID) references Customer (ID)
Hibernate: insert into Customer (NAME) values (?)
Hibernate: insert into ORDERS (CUSTOMER_ID, ORDER_NUMBER) values (?, ?)
Hibernate: insert into ORDERS (CUSTOMER_ID, ORDER_NUMBER) values (?, ?)