hibernate--一对多 多对一 双向关联 (重点!!!)

package com.bjsxt.hibernate;

import java.util.HashSet;
import java.util.Set;

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

@Entity
@Table(name="t_group")
public class Group {
private int id;
private String name;
private Set<User> users = new HashSet<User>();
@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;
}
@OneToMany(mappedBy="group")

public Set<User> getUsers() {
return users;
}
public void setUsers(Set<User> users) {
this.users = users;
}
}

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;
}
}

<?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 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>
<set name="users">
<key column="groupId"></key>
<one-to-many class="com.bjsxt.hibernate.User"/>
</set>
</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">

<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"></many-to-one>
</class>

</hibernate-mapping>