首先在oracle‘【你可以是其他数据库】中建三张表

<!--a表-->

create table a(
id number primary key,
name varchar2(50));

<!--b表-->

creata table b(
id number primary key,
xx varchar2(50));

<!--ab表-->

create table ab(
id number primary key,
a_id number references a(id),
b_id number references b(id));

之后建立映射

A.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.model.A" table="A" schema="DRDG">
        <id name="id" type="java.math.BigDecimal">
            <column name="ID" precision="22" scale="0" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" length="50" />
        </property>
        <set name="abs" inverse="true">
            <key>
                <column name="A_ID" precision="22" scale="0" />
            </key>
            <one-to-many class="com.model.Ab" />
        </set>
    </class>
</hibernate-mapping>

B.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.model.B" table="B" schema="DRDG">
        <id name="id" type="java.math.BigDecimal">
            <column name="ID" precision="22" scale="0" />
            <generator class="native" />
        </id>
        <property name="xx" type="java.lang.String">
            <column name="XX" length="50" />
        </property>
        <set name="abs" inverse="true">
            <key>
                <column name="B_ID" precision="22" scale="0" />
            </key>
            <one-to-many class="com.model.Ab" />
        </set>
    </class>
</hibernate-mapping>

AB.hbm.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.model.Ab" table="AB" schema="DRDG">
        <id name="id" type="java.math.BigDecimal">
            <column name="ID" precision="22" scale="0" />
            <generator class="native" />
        </id>
        <many-to-one name="b" class="com.model.B" fetch="select">
            <column name="B_ID" precision="22" scale="0" />
        </many-to-one>
        <many-to-one name="a" class="com.model.A" fetch="select">
            <column name="A_ID" precision="22" scale="0" />
        </many-to-one>
    </class>
</hibernate-mapping>

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">

<!-- Generated by MyEclipse Hibernate Tools.                   -->
<hibernate-configuration>

	<session-factory>
		<property name="dialect">
			org.hibernate.dialect.Oracle9Dialect
		</property>
		<property name="connection.url">
			jdbc:oracle:thin:@127.0.0.1:1521:orcl
		</property>
		<property name="connection.username">drdg</property>
		<property name="connection.password">zxcvbnm</property>
		<property name="show_sql">true</property>
		<property name="connection.driver_class">
			oracle.jdbc.driver.OracleDriver
		</property>
		<property name="myeclipse.connection.profile">
			oracle.jdbc.driver.OracleDriver
		</property>
		<mapping resource="com/model/Ab.hbm.xml" />
		<mapping resource="com/model/B.hbm.xml" />
		<mapping resource="com/model/A.hbm.xml" />

	</session-factory>

</hibernate-configuration>

测试类

package com.junit;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.junit.Test;

import com.model.Ab;
import com.util.HibernateSessionFactory;


public class T {

	@Test
	public void t(){
		Session session = HibernateSessionFactory.getSession();
		session.beginTransaction();
		
		List<Ab> ab = null;
		Query q =  session.createQuery("from Ab");
		ab = q.list();
		for(Ab a:ab){
			System.out.println(a.getA().getName());
		}
	}
	
	
}

下载地址：http://download.csdn.net/detail/yao__shun__yu/5087574