F005MyBatis學習筆記-MyBatis的多表關聯查詢

一、 概述

1、一對一

舉例：身份證號對人，一個身份證好只能對應一個人，一個人也只能對應一個身份證號，這就是一對一；

特例：Mybatis將多對一看做是一對一；

 

2、多對多

舉例：學生對老師，一個老師可以教多個學生，一個學生也可以被多個老師教，這就是多對多；

 

二、一對多案例演示

1、需求

用戶和賬戶：

一個用戶可以有多個賬戶；

一個賬戶只能屬於一個用戶（多個賬戶也可以屬於同一個用戶）；

 

2、步驟

第一步：建立兩張表：用戶表、賬戶表；

讓用戶表和賬戶表之間具備一對多的關係，需要在賬戶表中添加外鍵；

第二步：建立兩個實體類：用戶實體類和賬戶實體類；

讓用戶和賬戶的實體類體現出一對多的關係；

第三步：建立兩個配置文件：用戶的配置文件、賬戶的配置文件；

第四步：實現配置：當我們查詢用戶時，可以同時得到用戶下所包含賬戶的信息；當我們查詢賬戶時，可以得到賬戶所屬用戶的信息；

 

3、一對多代碼演示

SQL語句：

CREATE TABLE `account` (
  `ID` int(11) NOT NULL COMMENT '編號',
  `UID` int(11) default NULL COMMENT '用戶編號',
  `MONEY` double default NULL COMMENT '金額',
  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 {
    //查詢所有賬戶
    List<Account> findAll();
    //查詢所有賬戶帶user的用戶名和地址信息
    List<AccountUser> findAllAccount();
}

IUserDao:

package com.zibo.mybatis_crud.dao;

import com.zibo.mybatis_crud.domain.User;

import java.util.List;

public interface IUserDao {
    //查詢所有，同時獲取到用戶所有的賬戶信息
    List<User> findAll();
    //根據id查詢一條數據
    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;

    //一對多關係映射：主表實體應該包含從表實體的集合引用
    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">
    <!--    定義封裝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"/>
        <!--        一對一關係映射，配置封裝user的內容-->
        <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>
    <!--配置查詢所有-->
    <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>
    <!--查詢一條數據-->
    <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">
    <!-- 定義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對象中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>
    <!-- 查詢所有 -->
    <select id="findAll" resultMap="userAccountMap">
        select * from user u left outer join account a on u.id = a.uid
    </select>
    <!--查詢一條數據-->
    <select id="findById" parameterType="Integer" resultType="user">
        select * from user where id = #{隨便寫};
    </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>
        <!-- 單個別名定義 -->
<!--        <typeAlias alias="user" type="com.itheima.domain.User"/>-->
        <!-- 批量別名定義，掃描整個包下的類，別名爲類名（首字母大寫或小寫都可以） -->
        <package name="com.zibo.mybatis_crud.domain"/>
    </typeAliases>

    <!--    配置環境-->
    <environments default="mysql">
<!--        mysql的配置-->
        <environment id="mysql">
<!--            配置事務的類型-->
            <transactionManager type="JDBC">

            </transactionManager>
<!--            配置數據源（連接池）-->
            <dataSource type="POOLED">
<!--                配置數據庫的4個基本信息-->
                <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"/>-->
<!--        註冊指定包下的所有 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、讀取配置文件
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2、創建SqlSessionFactory工廠
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(in);
        //3、通過SqlSessionFactory工廠生產SqlSession對象
        sqlSession = factory.openSession(true);
        //4、使用SqlSession創建Dao接口的代理對象
        iUserDao = sqlSession.getMapper(IUserDao.class);
        iAccountDao = sqlSession.getMapper(IAccountDao.class);
    }
    @After
    public void end() throws IOException {
        //6、釋放資源
        sqlSession.close();
        in.close();
    }
    /**
     * 測試查詢所有
     */
    @Test
    public void testFindAll(){
        //5、使用代理對象執行方法
        List<User> users = iUserDao.findAll();
        for (User user : users) {
            System.out.println(user);
            System.out.println(user.getAccounts());
        }
    }
    @Test
    public void testFindById(){
        //5、使用代理對象執行方法
        User user = iUserDao.findById(45);
        System.out.println(user);
    }


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

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

文件位置結構圖：

 

三、多對多案例演示

1、需求

示例：用戶和角色

一個用戶可以有多個角色；

一個角色可以賦予多個用戶；

 

2、步驟

第一步：建立兩張表：用戶表、角色表；

讓用戶表和角色表具有多對多的關係，需要使用中間表，中間表中包含各自的主鍵，在中間表中是外鍵；

第二步：建立兩個實體類：用戶實體類和角色實體類；

讓用戶和角色的實體類體現出多對多的關係；

各自包含對方一個集合；

第三步：建立兩個配置文件：用戶的配置文件、角色的配置文件；

第四步：實現配置：當我們查詢用戶時，可以同時得到用戶下所包含角色的信息；當我們查詢角色時，可以得到賬戶所屬用戶的信息；

 

3、代碼演示

SQL:

CREATE TABLE `user` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(32) NOT NULL COMMENT '用戶名稱',
  `birthday` datetime default NULL COMMENT '生日',
  `sex` char(1) default NULL COMMENT '性別',
  `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','北京金燕龍'),(43,'小二王','2018-03-04 11:34:34','女','北京金燕龍'),(45,'傳智播客','2018-03-04 12:04:06','男','北京金燕龍'),(46,'老王','2018-03-07 17:37:26','男','北京'),(48,'小馬寶莉','2018-03-08 11:44:00','女','北京修正');


CREATE TABLE `role` (
  `ID` int(11) NOT NULL COMMENT '編號',
  `ROLE_NAME` varchar(30) default NULL COMMENT '角色名稱',
  `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,'院長','管理整個學院'),(2,'總裁','管理整個公司'),(3,'校長','管理整個學校');


CREATE TABLE `user_role` (
  `UID` int(11) NOT NULL COMMENT '用戶編號',
  `RID` int(11) NOT NULL COMMENT '角色編號',
  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 {
    //查詢所有，同時獲取到角色所有的用戶信息
    List<Role> findAll();
}

IUserDao：

package com.zibo.mybatis_crud.dao;

import com.zibo.mybatis_crud.domain.User;

import java.util.List;

public interface IUserDao {
    //查詢所有，同時獲取到用戶所有的角色信息
    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;

    //多對多關係映射
    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;

    //多對多
    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">
    <!-- 定義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>
    <!-- 查詢所有 -->
    <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">
    <!-- 定義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對象中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>
    <!-- 查詢所有 -->
    <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、讀取配置文件
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2、創建SqlSessionFactory工廠
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(in);
        //3、通過SqlSessionFactory工廠生產SqlSession對象
        sqlSession = factory.openSession(true);
        //4、使用SqlSession創建Dao接口的代理對象
        iUserDao = sqlSession.getMapper(IUserDao.class);
        iRoleDao = sqlSession.getMapper(IRoleDao.class);
    }
    @After
    public void end() throws IOException {
        //6、釋放資源
        sqlSession.close();
        in.close();
    }
    /**
     * 測試查詢所有
     */
    @Test
    public void testFindAll(){
        //5、使用代理對象執行方法
        List<User> users = iUserDao.findAll();
        for (User user : users) {
            System.out.println(user);
            System.out.println(user.getRoles());
        }
    }

    @Test
    public void testFindAll_R(){
        //5、使用代理對象執行方法
        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，見一對多代碼演示；