Mybatis框架(十一)：Mybatis的对象关系映射（二）

一、多对多关系映射的环境搭建

1、创建数据库表

CREATE DATABASE test;
 
CREATE TABLE `user` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(32) NOT NULL COMMENT '用户名称',
  `birthday` datetime default NULL COMMENT '生日',
  `sex` char(1) default NULL COMMENT '性别',
  `address` varchar(256) default NULL COMMENT '地址',
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (41,'老王','2018-02-27 17:47:08','男','北京');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (42,'小二王','2018-03-02 15:09:37','女','北京金燕龙');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (43,'小二王','2018-03-04 11:34:34','女','北京金燕龙');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (45,'传智播客','2018-03-04 12:04:06','男','北京金燕龙');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (46,'老王','2018-03-07 17:37:26','男','北京');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (48,'小马宝莉','2018-03-08 11:44:00','女','北京修正');

CREATE TABLE `role` (
  `ID` int(11) NOT NULL COMMENT '编号',
  `ROLE_NAME` varchar(30) default NULL COMMENT '角色名称',
  `ROLE_DESC` varchar(60) default NULL COMMENT '角色描述',
  PRIMARY KEY  (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `role`(`ID`,`ROLE_NAME`,`ROLE_DESC`) values (1,'院长','管理整个学院'),(2,'总裁','管理整个公司'),(3,'校长','管理整个学校');

CREATE TABLE `user_role` (
  `UID` int(11) NOT NULL COMMENT '用户编号',
  `RID` int(11) NOT NULL COMMENT '角色编号',
  PRIMARY KEY  (`UID`,`RID`),
  KEY `FK_Reference_10` (`RID`),
  CONSTRAINT `FK_Reference_10` FOREIGN KEY (`RID`) REFERENCES `role` (`ID`),
  CONSTRAINT `FK_Reference_9` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `user_role`(`UID`,`RID`) values (41,1),(45,1),(41,2);

2、创建maven工程并导入坐标

3、创建实体类、持久层dao接口

用户实体类User

package com.wedu.mybatis10.domain;

import java.io.Serializable;
import java.util.Date;

/**
 * 用户实体
 */
public class User implements Serializable {

    private Integer id;
    private String username;
    private String address;
    private String sex;
    private Date birthday;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", address='" + address + '\'' +
                ", sex='" + sex + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

角色实体类Role

package com.wedu.mybatis10.domain;

import java.io.Serializable;

/**
 * 角色实体
 */
public class Role implements Serializable {

    private Integer roleId;
    private String roleName;
    private String roleDesc;

    public Integer getRoleId() {
        return roleId;
    }

    public void setRoleId(Integer roleId) {
        this.roleId = roleId;
    }

    public String getRoleName() {
        return roleName;
    }

    public void setRoleName(String roleName) {
        this.roleName = roleName;
    }

    public String getRoleDesc() {
        return roleDesc;
    }

    public void setRoleDesc(String roleDesc) {
        this.roleDesc = roleDesc;
    }

    @Override
    public String toString() {
        return "Role{" +
                "roleId=" + roleId +
                ", roleName='" + roleName + '\'' +
                ", roleDesc='" + roleDesc + '\'' +
                '}';
    }
}

用户持久层接口IUserDao

package com.wedu.mybatis10.dao;

/**
 * 用户的持久层接口
 */
public interface IUserDao {

}

账户持久层接口IRoleDao

package com.wedu.mybatis10.dao;

/**
 * 角色的持久层接口
 */
public interface IRoleDao {

}

4、创建数据库配置文件：jdbc.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test?useSSL=true&useUnicode=true&characterEncoding=utf8
jdbc.username=root
jdbc.password=123456

5、创建日志文件：log4j.properties

# Set root category priority to INFO and its only appender to CONSOLE.
#log4j.rootCategory=INFO, CONSOLE            debug   info   warn error fatal
log4j.rootCategory=debug, CONSOLE, LOGFILE

# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE

# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n

# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=E:\\project\\axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n

6、创建配置文件：SqlMapConfig.xml

<?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>
    <!--引用外部的配置文件信息-->
    <properties resource="jdbc.properties"/>

    <!--配置别名-->
    <typeAliases>
        <package name="com.wedu.mybatis10.domain"/>
    </typeAliases>

    <!--配置环境-->
    <environments default="mysql">
        <environment id="mysql">
            <!--配置事务的类型-->
            <transactionManager type="JDBC"></transactionManager>
            <!--配置数据源-->
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>

    <!--配置映射文件的位置-->
    <mappers>
        <package name="com.wedu.mybatis10.dao" />
    </mappers>
</configuration>

7、创建测试类UserDaoTest和RoleDaoTest

测试类UserDaoTest

package com.wedu.mybatis10.dao;

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 org.junit.After;
import org.junit.Before;

/**
 * 多对多对象关系映射测试
 */
public class UserDaoTest {

    private SqlSession session;
    private IUserDao userDao;

    @Before
    public void init() throws Exception{
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("SqlMapConfig.xml"));
        session = factory.openSession();
        userDao = session.getMapper(IUserDao.class);
    }

    @After
    public void destroy() {
        session.close();
    }
}

测试类RoleDaoTest

package com.wedu.mybatis10.dao;

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 org.junit.After;
import org.junit.Before;

/**
 * 多对多对象关系映射测试
 */
public class RoleDaoTest {

    private SqlSession session;
    private IRoleDao roleDao;

    @Before
    public void init() throws Exception{
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("SqlMapConfig.xml"));
        session = factory.openSession();
        roleDao = session.getMapper(IRoleDao.class);
    }

    @After
    public void destroy() {
        session.close();
    }
}

二、mybatis基于XML的多对多关系映射的实现

1、创建映射文件：IUserDao.xml和IRoleDao.xml

IUserDao.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="com.wedu.mybatis10.dao.IUserDao">

</mapper>

IRoleDao.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="com.wedu.mybatis10.dao.IRoleDao">

</mapper>

2、配置多对多的关系映射

2.1、在User和Role的实体类中添加关联对象的属性

在User中配置关联对象属性

    //多对多的关系映射：一个用户可以具备多个角色
    private List<Role> roles;

    public List<Role> getRoles() {
        return roles;
    }

    public void setRoles(List<Role> roles) {
        this.roles = roles;
    }

在Role中配置关联对象属性

    //多对多的关系映射：一个角色可以赋予多个用户
    private List<User> users;

    public List<User> getUsers() {
        return users;
    }

    public void setUsers(List<User> users) {
        this.users = users;
    }

2.2、在IUserDao接口和IRoleDao接口中添加查询方法

在IUserDao中添加查询方法

    /**
     * 查询所有用户,同时获取到用户下所有角色的信息
     * @return
     */
    List<User> findAll();

在IRoleDao中添加查询方法

    /**
     * 查询所有角色,同时获取到角色下所有用户的信息
     */
    List<Role> findAll();

2.3、在IUserDao.xml和IRoleDao.xml中添加查询的sql语句

在IUserDao.xml中添加查询的sql语句

    <!--定义User的resultMap-->
    <resultMap id="userMap" type="user">
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="birthday" column="birthday"></result>
        <result property="sex" column="sex"></result>
        <result property="address" column="address"></result>
        <!-- 多对多关系映射：配置角色集合的映射 -->
        <collection property="roles" ofType="role">
            <id property="roleId" column="rid"></id>
            <result property="roleName" column="role_name"></result>
            <result property="roleDesc" column="role_desc"></result>
        </collection>
    </resultMap>

    <!-- 查询所有用户,，同时获取到用户下所有角色的信息 -->
    <select id="findAll" resultMap="userMap">
        select u.*,r.id as rid,r.role_name,r.role_desc from user u
        left outer join user_role ur  on u.id = ur.uid
        left outer join role r on r.id = ur.rid
    </select>

在IRoleDao.xml中添加查询的sql语句

   <!--定义role表的ResultMap-->
    <resultMap id="roleMap" type="role">
        <id property="roleId" column="rid"></id>
        <result property="roleName" column="role_name"></result>
        <result property="roleDesc" column="role_desc"></result>
        <!--多对多关系映射：配置用户集合的映射-->
        <collection property="users" ofType="user">
            <id column="id" property="id"></id>
            <result column="username" property="username"></result>
            <result column="birthday" property="birthday"></result>
            <result column="sex" property="sex"></result>
            <result column="address" property="address"></result>
        </collection>
    </resultMap>

    <!-- 查询所有角色,同时获取到角色下所有用户的信息 -->
    <select id="findAll" resultMap="roleMap">
        SELECT u.*,r.id as rid,r.role_name,r.role_desc FROM role r
        LEFT OUTER JOIN user_role ur ON r.id = ur.rid
        LEFT JOIN USER u ON u.id = ur.uid
    </select>

2.4、在UserDaoTest和RoleDaoTest添加测试方法

在UserDaoTest添加测试方法

    /**
     * 查询所有用户,，同时获取到用户下所有角色的信息
     */
    @Test
    public void testFindAll() {
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user);
            System.out.println(user.getRoles());
        }
    }

在RoleDaoTest添加测试方法

    /**
     * 查询所有角色
     */
    @Test
    public void testFindAll() {
        List<Role> roles = roleDao.findAll();
        for (Role role : roles) {
            System.out.println(role);
            System.out.println(role.getUsers());
        }
    }