MyBatis映射利用mysql left join 解决N+1查询问题

yanglgzh

　　1.权限是几乎每个系统都需要的
　　2.一般在用户请求某个url的时候，都需要验证用户是否拥有该url的访问权限
　　3.最简单的权限系统需要 用户表，角色表，用户角色表，权限表，角色权限表

　　

 

 

 

 

 

# Host: 127.0.0.1  (Version: 5.6.22)
# Date: 2015-04-09 10:52:58
# Generator: MySQL-Front 5.3  (Build 4.13)
/*!40101 SET NAMES utf8 */;
#
# Source for table "privilege"
#
CREATE TABLE `privilege` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
`url` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
#
# Data for table "privilege"
#
INSERT INTO `privilege` VALUES (1,'产品增加','/product/add'),(2,'产品删除','/product/delete'),(3,'产品修改','/product/update'),(4,'产品查询','/product/query');
#
# Source for table "role"
#
CREATE TABLE `role` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
#
# Data for table "role"
#
INSERT INTO `role` VALUES (1,'admin'),(2,'manager'),(3,'guest');
#
# Source for table "role_priv"
#
CREATE TABLE `role_priv` (
`role_id` int(11) NOT NULL,
`priv_id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
#
# Data for table "role_priv"
#
INSERT INTO `role_priv` VALUES (1,1),(2,1),(1,3);
#
# Source for table "user"
#
CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
#
# Data for table "user"
#
INSERT INTO `user` VALUES (1,'jack'),(2,'jaychang'),(3,'jasaon'),(4,'lucy'),(5,'marry');
#
# Source for table "user_role"
#
CREATE TABLE `user_role` (
`user_id` int(11) NOT NULL DEFAULT '0',
`role_id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
#
# Data for table "user_role"
#
INSERT INTO `user_role` VALUES (1,1),(1,3),(3,2),(2,2);
　　
　　4.表对应的实体类
　　放在了sample包下
　　

public class Privilege {
private Integer id;
private String name;
private String url;
...省略get,set方法
}
　　

public class User {
private Integer id;
private String name;
private List<Role> roles;
...省略get,set方法
}
　　

public class Role {
private Integer id;
private String name;
private List<Privilege> privileges;
...省略get,set方法
}
　　5.mybatis配置文件

<?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>
<typeAliases>
<typeAlias type="sample.User" alias="User" />
<typeAlias type="sample.Role" alias="Role" />
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://127.0.0.1:3306/temp" />
<property name="username" value="root" />
<property name="password" value="123456" />
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mybatis/mapper/UserMapper.xml" />
</mappers>
</configuration>
　　6.UserMapper.xml

<?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="sample.User">
<resultMap type="User" id="userResultMap">
<id property="id" column="user_id" />
<result property="name" column="user_name" />
<collection property="roles" ofType="sample.Role">
<result property="id" column="role_id"/>
<result property="name" column="role_name"/>
<collection property="privileges" ofType="sample.Privilege">
<result property="id" column="priv_id"/>
<result property="name" column="priv_name"/>
<result property="url" column="priv_url"/>
</collection>
</collection>
</resultMap>
<resultMap type="Role" id="roleResultMap">
<id property="id" column="role_id" />
<result property="name" column="role_name" />
<collection property="privileges" ofType="sample.Privilege">
<result property="id" column="priv_id"/>
<result property="name" column="priv_name"/>
<result property="url" column="priv_url"/>
</collection>
</resultMap>
<select id="selectUserById" parameterType="long" resultMap="userResultMap">
select u.id as user_id,u.name as user_name,r.id as role_id,
r.name as role_name,p.id as priv_id,p.name as priv_name,p.url as priv_url
from user u
left join user_role ur on u.id = ur.user_id
left join role r on r.id = ur.role_id
left join role_priv rp on r.id = rp.role_id
left join privilege p on p.id = rp.priv_id
where u.id = #{id}
</select>
</mapper>
　　

测试
List<User> users = sqlSession.selectList("selectUserById", 1L);
for (User u : users) {
System.out.println("用户名：" + u.getName());
List<Role> roles = u.getRoles();
if (null != roles) {
for (Role role : roles) {
System.out.println("    拥有角色：" + role.getName());
List<Privilege> privs = role.getPrivileges();
if (null != privs && privs.size() > 0) {
System.out.println("        该角色【" + role.getName()
+ "】，拥有的权限:");
for (Privilege priv : privs) {
System.out.println("            " + priv.getName()
+ "," + priv.getUrl());
}
}
}
}
}