hibernate_exercise-many- to-one(1)

多对一关系

1.创建t_user表、t_group表

2.在eclipse中创建对应的实体类

 package com.eneity;

 public class User {

     private int id;
     private String name;
     private Group group;//注意这里不是gid 而是group对象

     public User() {
         super();
         // TODO Auto-generated constructor stub
     }
     public int getId() {
         return id;
     }
     public void setId(int id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public Group getGroup() {
         return group;
     }
     public void setGroup(Group group) {
         this.group = group;
     }

 }

User.java

 package com.eneity;

 public class Group {

     private int id ;
     private String name;

     public Group() {
         super();
         // TODO Auto-generated constructor stub
     }
     public int getId() {
         return id;
     }
     public void setId(int id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }

 }

Group.java

3.写对应的xml映射文件

注意：写好对应的xml文件后要在主配置文件中添加映射

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 <!-- Generated 2018-4-8 16:35:46 by Hibernate Tools 3.4.0.CR1 -->
 <hibernate-mapping>
     <class name="com.eneity.User" table="t_user">
         <id name="id" type="int">
             <column name="ID" />
             <generator class="native" />
         </id>
         <property name="name" type="java.lang.String">
             <column name="NAME" />
         </property>
         <many-to-one name="group" class="com.eneity.Group" fetch="join">
             <column name="gid" />
         </many-to-one>
     </class>
 </hibernate-mapping>

com/eneity/User.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 <!-- Generated 2018-4-8 16:35:46 by Hibernate Tools 3.4.0.CR1 -->
 <hibernate-mapping>
     <class name="com.eneity.Group" table="t_group">
         <id name="id" type="int">
             <column name="ID" />
             <generator class="native" />
         </id>
         <property name="name" type="java.lang.String">
             <column name="NAME" />
         </property>
     </class>
 </hibernate-mapping>

com/eneity/Group.hbm.xml

主配置文件

 <?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>
         <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
         <property name="hibernate.connection.password">xzt521</property>
         <property name="hibernate.connection.url">jdbc:mysql://127.0.0.1:3306/myweb</property>
         <property name="hibernate.connection.username">xzt</property>
             <!-- 配置显示sql语句 -->
         <property name="show_sql">true</property>
         <!-- 以一定的格式输出语句 -->
         <property name="format_sql">true</property>
         <mapping resource="com/eneity/Group.hbm.xml"/>
         <mapping resource="com/eneity/User.hbm.xml"/>
     </session-factory>
 </hibernate-configuration>

hibernate.cfg.xml

4.写一个测试类

注意：如果只是要查询数据，只要开启session即可

要增删改的话，要开启事务管理

最后要提交事务（这样数据库中才会存进去数据）

关闭session

 package com.test;

 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 import org.hibernate.Transaction;
 import org.hibernate.cfg.Configuration;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;

 import com.eneity.Customers;
 import com.eneity.Group;
 import com.eneity.Order;
 import com.eneity.User;

 public class Test1 {
     private SessionFactory buildSessionFactory;
     private Session Session;
     private Transaction Transaction;

     @Before
     public void before() {
         Configuration cfg = new Configuration().configure();
         buildSessionFactory = cfg.buildSessionFactory();
         Session = buildSessionFactory.openSession();
         Transaction = Session.beginTransaction();
         System.out.println(Session);

     }

     @Test
     public void test1() {
         // TODO Auto-generated method stub

         Group group = new Group();
         group.setName("duhao");
         User user = new User();
         user.setName("jiunan");
         user.setGroup(group);
         Session.save(group);
         Session.save(user);

     }

     @After
     public void after() {
         Transaction.commit();
         Session.close();

     }
 }

Test1.java