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;
    }
    

}

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;
    }

}

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>

<?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>

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>

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();
        
    }
}