hibernate--多对一单向关联 (重点!!!)

一个用户组包含多个用户, 每个用户属于一个组.

一个人可以有多个车, 每个车属于一个人.

一个人有很多梦想, 一个特定的梦想属于一个人.

错误做法:

person里 有 personid, personname, dreamid

dream里有id, dreamdescr

会出现冗余, 因为是一对多

personid  personname   dreamid

1           zhangsan       1

1           zhangsan       2

dreamid    dreamdescr

1　　　　   earn money

2              eat a lot

下面做人和组的关系,  一个group有很多user, 一个user只属于一个group, 所以group是 一   user是多

group.java:

package com.bjsxt.hibernate;

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

@Entity
@Table(name="t_group")
public class Group {
	private int id;
	private String name;
	@Id
	@GeneratedValue
	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;
	}
}

user.java:

里面创建一个group对象, 是多对一的单项

package com.bjsxt.hibernate;

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

@Entity
@Table(name="t_user")
public class User {
	private int id;
	private String name;
	private Group group;
	@ManyToOne

	public Group getGroup() {
		return group;
	}
	public void setGroup(Group group) {
		this.group = group;
	}
	@Id
	@GeneratedValue
	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;
	}
}

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>

        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost/hibernate</property>
        <property name="connection.username">root</property>
        <property name="connection.password">linda0213</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
       <!--
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:SXT</property>
        <property name="connection.username">scott</property>
        <property name="connection.password">tiger</property>
      	<property name="dialect">org.hibernate.dialect.OracleDialect</property>
       -->

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

        <!-- Drop and re-create the database schema on startup
        <property name="hbm2ddl.auto">update</property>
		 -->

        <mapping class="com.bjsxt.hibernate.Group"/>
		<mapping class="com.bjsxt.hibernate.User"/>

		   <!--
		 <mapping resource="com/bjsxt/hibernate/Group.hbm.xml"/>
		 <mapping resource="com/bjsxt/hibernate/User.hbm.xml"/>-->

    </session-factory>

</hibernate-configuration>

XML方式:

group是一, 不需要改什么:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
	<class name="com.bjsxt.hibernate.Group" table="t_group">
		<id name="id">
			<generator class="native"></generator>
		</id>
		<property name="name"></property>
    </class>
</hibernate-mapping>

　　

user是多, 需要设置:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
	<class name="com.bjsxt.hibernate.User" table="t_user">
		<id name="id">
			<generator class="native"></generator>
		</id>
		<property name="name"></property>
		<many-to-one name="group" column="groupId" />
    </class>
</hibernate-mapping>

　　

　test文件:

package com.bjsxt.hibernate;

import java.util.Date;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

public class HibernateORMappingTest {
	private static SessionFactory sessionFactory;

	//@BeforeClass
	public static void beforeClass() {
			sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
	}
	//@AfterClass
	public static void afterClass() {
		sessionFactory.close();
	}

	@Test
	public void testSchemaExport() {
		new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
	}
	public static void main(String[] args) {
		beforeClass();
	}
}