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mybatis3.0添加了association和collection标签专门用于对多个相关实体类数据进行级联查询，但仍不支持多个相关实体类数据的级联保存和级联删除操作。因此在进行实体类多对多映射表设计时，需要专门建立一个关联对象类对相关实体类的关联关系进行描述。下文将以“User”和“Group"两个实体类之间的多对多关联映射为例进行CRUD操作。

建立user表，对应实体类"User"，建表语句如下：
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CREATE TABLE `user` (`id` int(11) NOT NULL auto_increment,`name` varchar(40) collate utf8_unicode_ci default NULL,`password` varchar(20) collate utf8_unicode_ci default NULL,`createtime` timestamp NULL default CURRENT_TIMESTAMP,PRIMARY KEY  (`id`)
)

建立group_info表，对应实体类"Group"，建表语句如下：

CREATE TABLE `group_info` (`id` int(11) NOT NULL auto_increment,`name` varchar(40) collate utf8_unicode_ci default NULL,`createdate` timestamp NULL default CURRENT_TIMESTAMP,`state` int(1) default '0' COMMENT '0:可见;1:不可见',PRIMARY KEY  (`id`)
)

建立user_group表，对应实体类"UserGroupLink"(该类为User和Group两个实体类之间的关系描述)，建表语句如下：

CREATE TABLE `user_group` (`user_id` int(11) default NULL,`group_id` int(11) default NULL,`createdate` timestamp NULL default CURRENT_TIMESTAMP,KEY `FK_user_group_user_id` (`user_id`),KEY `FK_user_group_group_id` (`group_id`),CONSTRAINT `FK_user_group_group_id` FOREIGN KEY (`group_id`) REFERENCES `group_info` (`id`),CONSTRAINT `FK_user_group_user_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`)
)

建立实体类User，代码如下：

package com.xxt.ibatis.dbcp.domain;import java.util.Date;
import java.util.List;/*** @describe: User实体类* @author:    Nirvana* @version:   V1.0  2011-3-11下午06:06:49 create*/public class User {private long id;private String name;private String password;private Date createTime;private List<Group> group;public Date getCreateTime() {return createTime;}public void setCreateTime(Date createTime) {this.createTime = createTime;}public long getId() {return id;}public void setId(long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public List<Group> getGroup() {return group;}public void setGroup(List<Group> group) {this.group = group;}
}

建立实体类Group,代码如下：

package com.xxt.ibatis.dbcp.domain;import java.util.Date;
import java.util.List;/*** @describe: Group实体类* @author: Nirvana* @version: V1.0 2011-3-7下午08:10:29 create*/
public class Group {private long id;private String name; // 组名private Date createTime;private int state; // 0可见状态 1不可见状态private List<User> user;public Date getCreateTime() {return createTime;}public void setCreateTime(Date createTime) {this.createTime = createTime;}public long getId() {return id;}public void setId(long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getState() {return state;}public void setState(int state) {this.state = state;}public List<User> getUser() {return user;}public void setUser(List<User> user) {this.user = user;}}

建立实体类UserGroupLink，用于描述User和Group之间的对应关系，代码如下：

package com.xxt.ibatis.dbcp.domain;import java.util.Date;/*** @describe: 描述User和Group之间的映射关系* @author: Nirvana* @version: V1.0 2011-3-11下午02:57:52 create*/
public class UserGroupLink {private User user;private Group group;private Date createTime;public Date getCreateTime() {return createTime;}public void setCreateTime(Date createTime) {this.createTime = createTime;}public Group getGroup() {return group;}public void setGroup(Group group) {this.group = group;}public User getUser() {return user;}public void setUser(User user) {this.user = user;}
}

建立user实体类的映射文件user.map.xml，代码如下：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.xxt.ibatis.dbcp.domain.User"><resultMap type="User" id="userMap"><id property="id" column="id" /><result property="name" column="name" /><result property="password" column="password" /><result property="createTime" column="createtime" /></resultMap><resultMap type="User" id="userGroupMap" extends="userMap"><collection property="groups" ofType="Group"><id property="id" column="goupId" /><result property="name" column="groupName" /><result property="state" column="state" /><result property="createTime" column="groupCreateTime" /></collection></resultMap><!-- 根据user表中的id查询用户信息 --><select id="selectUser" parameterType="long" resultMap="userMap">select * from user where id = #{id}</select><!-- 根据user表中的id查询用户和组信息 --><select id="selectUserGroup" parameterType="long"resultMap="userGroupMap">select u.id,u.name,u.password,u.createtime, gi.id asgoupId,gi.name as groupName, gi.createdate as groupCreateTime,gi.state from user u left join user_group ug on u.id=ug.user_idleft join group_info gi on ug.group_id=gi.id where u.id = #{id}</select><!-- 插入用户信息 --><insert id="saveUser" parameterType="User" keyProperty="id"useGeneratedKeys="true">insert into user(name,password) values(#{name},#{password})</insert><!-- 保存用户和组之间的关系信息 --><insert id="saveRelativity" parameterType="UserGroupLink">insert into user_group(user_id,group_id)values(#{user.id},#{group.id})</insert><select id="selectAllUser" resultMap="userMap">select * from user</select></mapper>

建立group实体类的映射文件group.map.xml，代码如下:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.xxt.ibatis.dbcp.domain.Group"><resultMap type="Group" id="groupMap"><id property="id" column="id" /><result property="name" column="name" /><result property="createTime" column="createdate" /></resultMap><resultMap type="Group" id="groupUserMap" extends="groupMap"><collection property="users" ofType="User"><id property="id" column="userId" /><result property="name" column="userName" /><result property="password" column="password" /><result property="createTime" column="userCreateTime" /></collection></resultMap><!-- 根据Group表中的id或name查询组信息和组内用户信息 --><select id="selectGroupUser" parameterType="Group"resultMap="groupUserMap">select u.id as userId,u.name as userName,u.password,u.createtime as userCreateTime,gi.id,gi.name,gi.createdate,gi.state from group_info gi leftjoin user_group ug on gi.id=ug.group_id left join user u onug.user_id=u.id<where><!--当id为初始值0，不再使用id作为查询条件 --><if test="id != 0  ">gi.id=#{id}</if><!-- 当name为空或为空串时，不再使用name作为查询条件 --><if test="name != null and name != ''">or gi.name = #{name}</if></where></select><!-- 根据id查询group组信息 --><select id="selectGroup" parameterType="Date"resultMap="groupMap">select * from group_info where id=#{group_id}</select><!--根据name查询group组信息  --><select id="getGroupByName" parameterType="String"resultMap="groupMap">select * from group_info where name=#{name}</select><!-- 插入组信息 --><insert id="saveGroup" parameterType="Group" keyProperty="id"useGeneratedKeys="true">insert into group_info(name) values(#{name})</insert><!-- 删除组与组内成员之间的对应关系 --><delete id="deleteGroupUser" parameterType="UserGroupLink">delete from user_group<where><if test="user.id != 0">user_id = #{user.id}</if><if test="group.id != 0">and group_id = #{group.id}</if></where></delete><!--根据组id或者组name删除组信息 --><delete id="deleteGroup" parameterType="Group">delete from group_info<where><if test="id!=0">id=#{id}</if><if test="name!=null || name!=''">and name=#{name}</if></where></delete><!-- 更新根据组id或者组name更新组状态 --><update id="updateGroupState" parameterType="Group">update group_info set state=#{state}<where><if test="id!=0">id=#{id}</if><if test="name!=null || name!=''">and name=#{name}</if></where></update>
</mapper>

建立ibatis总配置文件salMapConfig.xml,代码如下：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><properties resource="jdbc.properties" /><typeAliases><typeAlias type="com.xxt.ibatis.dbcp.domain.User" alias="User" /><typeAlias type="com.xxt.ibatis.dbcp.domain.Group"alias="Group" /><typeAlias type="com.xxt.ibatis.dbcp.domain.UserGroupLink"alias="UserGroupLink" /></typeAliases><environments default="development"><environment id="development"><transactionManager type="JDBC" /><dataSource type="UNPOOLED"><property name="driver" value="${driver}" /><property name="url" value="${url}" /><property name="username" value="${username}" /><property name="password" value="${password}" /></dataSource></environment></environments><mappers><mapper resource="com/xxt/ibatis/dbcp/domain/user.map.xml" /><mapper resource="com/xxt/ibatis/dbcp/domain/group.map.xml" /></mappers>
</configuration>

测试用例，代码如下：

package com.xxt.ibatis.dbcp.test;import java.io.Reader;
import java.text.SimpleDateFormat;
import java.util.List;import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;import com.xxt.ibatis.dbcp.domain.Group;
import com.xxt.ibatis.dbcp.domain.User;
import com.xxt.ibatis.dbcp.domain.UserGroupLink;/*** @describe: 测试用例* @author:    Nirvana* @version:   V1.0  2011-3-4下午03:21:17 create*/
public class IbatisUserTest {private final static String IBATIS_CONFIG_XML  = "sqlMapConfig.xml"; private static SqlSession session;private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd k:mm:ss");@BeforeClasspublic static void setUpBeforeClass() throws Exception {Reader reader = Resources.getResourceAsReader(IBATIS_CONFIG_XML);  //读取ibatis配置文件SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);session = sqlMapper.openSession(true);session.commit(false); //将默认提交事务属性设置为否}//保存用户信息@Testpublic void saveUserTest(){User user = new User();user.setName("张三");user.setPassword("123456");session.insert("com.xxt.ibatis.dbcp.domain.User.saveUser", user);}//获取用户信息@Testpublic void getUserTest(){User user = (User) session.selectOne("com.xxt.ibatis.dbcp.domain.User.selectUser", 1L);System.out.println("用户名： "+user.getName());System.out.println("用户密码:  "+user.getPassword());System.out.println("用户创建日期："+sdf.format(user.getCreateTime()));}//获取用户和用户所在组信息@Testpublic void getUserAndGroupTest(){User  user =  (User)session.selectOne("com.xxt.ibatis.dbcp.domain.User.selectUserGroup", 4L);System.out.println(user.getName() +"所属组信息:");for(Group group : user.getGroups() ){System.out.println("   组名:"+group.getName()+"，组创建时间:"+sdf.format(group.getCreateTime()));}}//保存用户和用户所在组信息//当用户所在组不存在时，创建该组，并生成映射关系@Testpublic void saveUserAndGroupTest(){User user = new User();user.setName("无常鬼");user.setPassword("wuchang");session.insert("com.xxt.ibatis.dbcp.domain.User.saveUser", user);Group groupImpl = (Group)session.selectOne("com.xxt.ibatis.dbcp.domain.Group.getGroupByName","用户组4");//获取组实例UserGroupLink ugl = new UserGroupLink();//声明User和Group实体间映射关系实例//查询到的组实例为空时的逻辑处理if(groupImpl == null){Group group = new Group();group.setName("用户组4");session.insert("com.xxt.ibatis.dbcp.domain.Group.saveGroup", group);//持久化创建好的组实例//设置映射关系实例相关的属性ugl.setUser(user);ugl.setGroup(group);session.insert("com.xxt.ibatis.dbcp.domain.User.saveRelativity",ugl);//持久化映射关系实力}else{ugl.setGroup(groupImpl);ugl.setUser(user);session.insert("com.xxt.ibatis.dbcp.domain.User.saveRelativity",ugl);}}//删除组信息的同时，取消组内所有的成员与该组的关联关系@Testpublic void deleteGroupTest(){Group group = new Group();//group.setId(1L);  //以组id作为查询条件group.setName("用户组1"); //以组name作为查询条件Group groupImpl = (Group)session.selectOne("com.xxt.ibatis.dbcp.domain.Group.selectGroupUser",group);//获取组实例//组实例存在时if(groupImpl != null){List<User> users = groupImpl.getUsers();//查看用户组1中是否存在用户if(users != null && users.size() > 0){//存在用户时，先删除组与用户的对应关系UserGroupLink ugl = new UserGroupLink();for(User user : users){ugl.setUser(user);ugl.setGroup(groupImpl);session.delete("com.xxt.ibatis.dbcp.domain.Group.deleteGroupUser",ugl );} }//删除组信息session.delete("com.xxt.ibatis.dbcp.domain.Group.deleteGroup", groupImpl);}else{throw new RuntimeException("查询的组不存在!!");}}//更新组状态，当组状态由可见状态变成不可见时，取消该组下的用户与该组的映射关系@Testpublic void updateGroupStateTest(){Group group = new Group();group.setName("用户组2");Group groupImpl = (Group) session.selectOne("com.xxt.ibatis.dbcp.domain.Group.selectGroupUser",group);if(groupImpl != null){int state = groupImpl.getState() == 1 ? 0 : 1;//组状态由0变成1时，即由可见变为不可见if(state == 1){List<User> users = groupImpl.getUsers();//查看用户组2中是否存在用户if(users != null && users.size() > 0){//存在用户时，删除组与用户的对应关系UserGroupLink ugl = new UserGroupLink();for(User user : users){ugl.setUser(user);ugl.setGroup(groupImpl);session.delete("com.xxt.ibatis.dbcp.domain.Group.deleteGroupUser",ugl );} }} //更新组状态groupImpl.setState(state);}else{throw new RuntimeException("查询的组不存在!!");}}@AfterClasspublic static void tearDownAfterClass() throws Exception {if(session != null){session.commit(); //提交事务session.close(); //关闭连接}}
}