F005MyBatis学习笔记-MyBatis的多表关联查询

一、 概述

1、一对一

举例：身份证号对人，一个身份证好只能对应一个人，一个人也只能对应一个身份证号，这就是一对一；

特例：Mybatis将多对一看做是一对一；

 

2、多对多

举例：学生对老师，一个老师可以教多个学生，一个学生也可以被多个老师教，这就是多对多；

 

二、一对多案例演示

1、需求

用户和账户：

一个用户可以有多个账户；

一个账户只能属于一个用户（多个账户也可以属于同一个用户）；

 

2、步骤

第一步：建立两张表：用户表、账户表；

让用户表和账户表之间具备一对多的关系，需要在账户表中添加外键；

第二步：建立两个实体类：用户实体类和账户实体类；

让用户和账户的实体类体现出一对多的关系；

第三步：建立两个配置文件：用户的配置文件、账户的配置文件；

第四步：实现配置：当我们查询用户时，可以同时得到用户下所包含账户的信息；当我们查询账户时，可以得到账户所属用户的信息；

 

3、一对多代码演示

SQL语句：

CREATE TABLE `account` (
  `ID` int(11) NOT NULL COMMENT '编号',
  `UID` int(11) default NULL COMMENT '用户编号',
  `MONEY` double default NULL COMMENT '金额',
  PRIMARY KEY  (`ID`),
  KEY `FK_Reference_8` (`UID`),
  CONSTRAINT `FK_Reference_8` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;



insert  into `account`(`ID`,`UID`,`MONEY`) values (1,46,1000),(2,45,1000),(3,46,2000);

pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>mybatis0203</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.3</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13-beta-3</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

</project>

IAccountDao:

package com.zibo.mybatis_crud.dao;

import com.zibo.mybatis_crud.domain.Account;
import com.zibo.mybatis_crud.domain.AccountUser;

import java.util.List;

public interface IAccountDao {
    //查询所有账户
    List<Account> findAll();
    //查询所有账户带user的用户名和地址信息
    List<AccountUser> findAllAccount();
}

IUserDao:

package com.zibo.mybatis_crud.dao;

import com.zibo.mybatis_crud.domain.User;

import java.util.List;

public interface IUserDao {
    //查询所有，同时获取到用户所有的账户信息
    List<User> findAll();
    //根据id查询一条数据
    User findById(Integer userId);
}

Account:

package com.zibo.mybatis_crud.domain;

public class Account {
    private Integer id;
    private Integer uid;
    private double money;

    private User user;

    public Integer getId() {
        return id;
    }

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

    public Integer getUid() {
        return uid;
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public double getMoney() {
        return money;
    }

    public void setMoney(double money) {
        this.money = money;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    @Override
    public String toString() {
        return "Account{" +
                "id=" + id +
                ", uid=" + uid +
                ", money=" + money +
                '}';
    }
}

AccountUser:

package com.zibo.mybatis_crud.domain;

public class AccountUser extends Account {
    private String username;
    private String address;

    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;
    }

    @Override
    public String toString() {
        return super.toString() + "      AccountUser{" +
                "username='" + username + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

User:

package com.zibo.mybatis_crud.domain;

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

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    //一对多关系映射：主表实体应该包含从表实体的集合引用
    private List<Account> accounts;

    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 Date getBirthday() {
        return birthday;
    }

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

    public String getSex() {
        return sex;
    }

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

    public String getAddress() {
        return address;
    }

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

    public List<Account> getAccounts() {
        return accounts;
    }

    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }

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

IAccountDao.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.zibo.mybatis_crud.dao.IAccountDao">
    <!--    定义封装account和user的resultMap-->
    <resultMap id="accountUserMap" type="account">
        <id property="id" column="aid"/>
        <result property="uid" column="uid"/>
        <result property="money" column="money"/>
        <!--        一对一关系映射，配置封装user的内容-->
        <association property="user" column="uid" javaType="user">
            <id property="id" column="id"/>
            <result property="username" column="username"/>
            <result property="address" column="address"/>
            <result property="sex" column="sex"/>
            <result property="birthday" column="birthday"/>
        </association>
    </resultMap>
    <!--配置查询所有-->
    <select id="findAll" resultMap="accountUserMap">
        select u.*,a.id as aid,a.uid,a.money from account a,user u where u.id = a.uid;
    </select>
    <!--查询一条数据-->
    <select id="findAllAccount" resultType="accountUser">
        select a.*,u.username,u.address from account a,user u where u.id = a.uid;
    </select>
</mapper>

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.zibo.mybatis_crud.dao.IUserDao">
    <!-- 定义User的resultMap-->
    <resultMap id="userAccountMap" type="user">
        <id property="id" column="id"/>
        <result property="username" column="username"/>
        <result property="address" column="address"/>
        <result property="sex" column="sex"/>
        <result property="birthday" column="birthday"/>
        <!-- 配置user对象中accounts集合的映射 -->
        <collection property="accounts" ofType="account">
            <id column="aid" property="id"/>
            <result column="uid" property="uid"/>
            <result column="money" property="money"/>
        </collection>
    </resultMap>
    <!-- 查询所有 -->
    <select id="findAll" resultMap="userAccountMap">
        select * from user u left outer join account a on u.id = a.uid
    </select>
    <!--查询一条数据-->
    <select id="findById" parameterType="Integer" resultType="user">
        select * from user where id = #{随便写};
    </select>
</mapper>

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=d:\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

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>
    <!-- 在 SqlMapConfig.xml 中配置： -->
    <typeAliases>
        <!-- 单个别名定义 -->
<!--        <typeAlias alias="user" type="com.itheima.domain.User"/>-->
        <!-- 批量别名定义，扫描整个包下的类，别名为类名（首字母大写或小写都可以） -->
        <package name="com.zibo.mybatis_crud.domain"/>
    </typeAliases>

    <!--    配置环境-->
    <environments default="mysql">
<!--        mysql的配置-->
        <environment id="mysql">
<!--            配置事务的类型-->
            <transactionManager type="JDBC">

            </transactionManager>
<!--            配置数据源（连接池）-->
            <dataSource type="POOLED">
<!--                配置数据库的4个基本信息-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/zibo?serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="zibo15239417242"/>
            </dataSource>
        </environment>
    </environments>
<!--    指定映射配置文件的位置-->
    <mappers>
<!--        <mapper resource="com/zibo/mybatis_crud/dao/IUserDao.xml"/>-->
<!--        注册指定包下的所有 mapper 接口-->
        <package name="com.zibo.mybatis_crud.dao"/>
    </mappers>
</configuration>

Main:

package com.zibo.mybatis_crud;

import com.zibo.mybatis_crud.dao.IAccountDao;
import com.zibo.mybatis_crud.dao.IUserDao;
import com.zibo.mybatis_crud.domain.Account;
import com.zibo.mybatis_crud.domain.AccountUser;
import com.zibo.mybatis_crud.domain.User;
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;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Main {
    private InputStream in;
    private SqlSession sqlSession;
    private IUserDao iUserDao;
    private IAccountDao iAccountDao;
    /**
     * 初始化
     */
    @Before
    public void init() throws IOException {
        //1、读取配置文件
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2、创建SqlSessionFactory工厂
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(in);
        //3、通过SqlSessionFactory工厂生产SqlSession对象
        sqlSession = factory.openSession(true);
        //4、使用SqlSession创建Dao接口的代理对象
        iUserDao = sqlSession.getMapper(IUserDao.class);
        iAccountDao = sqlSession.getMapper(IAccountDao.class);
    }
    @After
    public void end() throws IOException {
        //6、释放资源
        sqlSession.close();
        in.close();
    }
    /**
     * 测试查询所有
     */
    @Test
    public void testFindAll(){
        //5、使用代理对象执行方法
        List<User> users = iUserDao.findAll();
        for (User user : users) {
            System.out.println(user);
            System.out.println(user.getAccounts());
        }
    }
    @Test
    public void testFindById(){
        //5、使用代理对象执行方法
        User user = iUserDao.findById(45);
        System.out.println(user);
    }


    @Test
    public void testFindAll_A(){
        //5、使用代理对象执行方法
        List<Account> accounts = iAccountDao.findAll();
        for (Account account : accounts) {
            System.out.println(account);
            System.out.println(account.getUser());
        }
    }

    @Test
    public void testFindAllAccount_A(){
        //5、使用代理对象执行方法
        List<AccountUser> accounts = iAccountDao.findAllAccount();
        for (AccountUser account : accounts) {
            System.out.println(account);
        }
    }
}

文件位置结构图：

 

三、多对多案例演示

1、需求

示例：用户和角色

一个用户可以有多个角色；

一个角色可以赋予多个用户；

 

2、步骤

第一步：建立两张表：用户表、角色表；

让用户表和角色表具有多对多的关系，需要使用中间表，中间表中包含各自的主键，在中间表中是外键；

第二步：建立两个实体类：用户实体类和角色实体类；

让用户和角色的实体类体现出多对多的关系；

各自包含对方一个集合；

第三步：建立两个配置文件：用户的配置文件、角色的配置文件；

第四步：实现配置：当我们查询用户时，可以同时得到用户下所包含角色的信息；当我们查询角色时，可以得到账户所属用户的信息；

 

3、代码演示

SQL:

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'),(42,'小二王','2018-03-02 15:09:37','女','北京金燕龙'),(43,'小二王','2018-03-04 11:34:34','女','北京金燕龙'),(45,'传智播客','2018-03-04 12:04:06','男','北京金燕龙'),(46,'老王','2018-03-07 17:37:26','男','北京'),(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);

IRoleDao：

package com.zibo.mybatis_crud.dao;

import com.zibo.mybatis_crud.domain.Role;

import java.util.List;

public interface IRoleDao {
    //查询所有，同时获取到角色所有的用户信息
    List<Role> findAll();
}

IUserDao：

package com.zibo.mybatis_crud.dao;

import com.zibo.mybatis_crud.domain.User;

import java.util.List;

public interface IUserDao {
    //查询所有，同时获取到用户所有的角色信息
    List<User> findAll();
}

Role：

package com.zibo.mybatis_crud.domain;

import java.io.Serializable;
import java.util.List;

public class Role implements Serializable {
    private Integer roleId;
    private String roleName;
    private String roleDesc;

    //多对多关系映射
    private List<User> users;

    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;
    }

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

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

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

User：

package com.zibo.mybatis_crud.domain;

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

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    //多对多
    private List<Role> roles;

    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 Date getBirthday() {
        return birthday;
    }

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

    public String getSex() {
        return sex;
    }

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

    public String getAddress() {
        return address;
    }

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

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

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

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


}

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.zibo.mybatis_crud.dao.IRoleDao">
    <!-- 定义User的resultMap-->
    <resultMap id="RoleMap" type="role">
        <id property="roleId" column="rid"/>
        <result property="roleName" column="role_name"/>
        <result property="roleDesc" column="role_desc"/>
        <collection property="users" ofType="user">
            <id property="id" column="id"/>
            <result property="username" column="username"/>
            <result property="address" column="address"/>
            <result property="sex" column="sex"/>
            <result property="birthday" column="birthday"/>
        </collection>
    </resultMap>
    <!-- 查询所有 -->
    <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 outer join user u on u.id = ur.uid;
    </select>
</mapper>

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.zibo.mybatis_crud.dao.IUserDao">
    <!-- 定义User的resultMap-->
    <resultMap id="userMap" type="user">
        <id property="id" column="id"/>
        <result property="username" column="username"/>
        <result property="address" column="address"/>
        <result property="sex" column="sex"/>
        <result property="birthday" column="birthday"/>
        <!-- 配置user对象中accounts集合的映射 -->
        <collection property="roles" ofType="role">
            <id property="roleId" column="rid"/>
            <result property="roleName" column="role_name"/>
            <result property="roleDesc" column="role_desc"/>
        </collection>
    </resultMap>
    <!-- 查询所有 -->
    <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 ur.RID = r.ID;
    </select>
</mapper>

Main:

package com.zibo.mybatis_crud;

import com.zibo.mybatis_crud.dao.IRoleDao;
import com.zibo.mybatis_crud.dao.IUserDao;
import com.zibo.mybatis_crud.domain.Role;
import com.zibo.mybatis_crud.domain.User;
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;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Main {
    private InputStream in;
    private SqlSession sqlSession;
    private IUserDao iUserDao;
    private IRoleDao iRoleDao;
    /**
     * 初始化
     */
    @Before
    public void init() throws IOException {
        //1、读取配置文件
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2、创建SqlSessionFactory工厂
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(in);
        //3、通过SqlSessionFactory工厂生产SqlSession对象
        sqlSession = factory.openSession(true);
        //4、使用SqlSession创建Dao接口的代理对象
        iUserDao = sqlSession.getMapper(IUserDao.class);
        iRoleDao = sqlSession.getMapper(IRoleDao.class);
    }
    @After
    public void end() throws IOException {
        //6、释放资源
        sqlSession.close();
        in.close();
    }
    /**
     * 测试查询所有
     */
    @Test
    public void testFindAll(){
        //5、使用代理对象执行方法
        List<User> users = iUserDao.findAll();
        for (User user : users) {
            System.out.println(user);
            System.out.println(user.getRoles());
        }
    }

    @Test
    public void testFindAll_R(){
        //5、使用代理对象执行方法
        List<Role> roles = iRoleDao.findAll();
        for (Role role : roles) {
            System.out.println(role);
            System.out.println(role.getUsers());
        }
    }
}

其他配置文件等，见一对多代码演示；