mybaits基于xml的实现数据多表关联的查询

其他 2021-03-07 19:52:54 阅读次数: 0

0.概述 

一.1对1的关系

背景描述：订单表和用户表是1对1的关系，1个订单只能隶属于1个用户。

1.1 新建工程

数据库脚本：

1.tb_orders表

CREATE TABLE `tb_orders` (
  `id` int(11) NOT NULL,
  `order_time` datetime NOT NULL,
  `total` double(255,0) NOT NULL,
  `uid` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

 2.tb_users表

CREATE TABLE `tb_users` (
  `id` int(11) NOT NULL,
  `user_name` varchar(255) DEFAULT NULL,
  `birthday` datetime DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

1.2 配置pom文件中的依赖

 <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.13</version>
      <scope>test</scope>
    </dependency>
    <!--mywql dueong  -->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.32</version>
    </dependency>
    <!--mybaits -->
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.4.5</version>
    </dependency>
    <!-- log4j-->
    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.17</version>
    </dependency>
    <!-- 分页插件-->
    <dependency>
      <groupId>com.github.pagehelper</groupId>
      <artifactId>pagehelper</artifactId>
      <version>3.7.5</version>
    </dependency>
    <dependency>
      <groupId>com.github.jsqlparser</groupId>
      <artifactId>jsqlparser</artifactId>
      <version>0.9.1</version>
    </dependency>

1.3 实体层

1.orders实体

package com.ljf.mybaits.relation.mapping.domain;

import java.util.Date;

/**
 * @ClassName: Orders
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/17 21:30:37 
 * @Version: V1.0
 **/
public class Orders {
    private int id;
    private Date orderTime;
    private double total;

    //当前订单属于哪一个用户
    private Users user;

    public int getId() {
        return id;
    }

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

    public Date getOrderTime() {
        return orderTime;
    }

    public void setOrderTime(Date orderTime) {
        this.orderTime = orderTime;
    }

    public double getTotal() {
        return total;
    }

    public void setTotal(double total) {
        this.total = total;
    }

    public Users getUser() {
        return user;
    }

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

    @Override
    public String toString() {
        return "Orders{" +
                "id=" + id +
                ", orderTime=" + orderTime +
                ", total=" + total +
                ", user=" + user +
                '}';
    }
}

2.users实体

package com.ljf.mybaits.relation.mapping.domain;

import java.util.Date;

/**
 * @ClassName: Users
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/17 21:30:28 
 * @Version: V1.0
 **/
public class Users {
    private int id;
    private String userName;
    private Date birthday;

    public int getId() {
        return id;
    }

    public void setId(int 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;
    }

    @Override
    public String toString() {
        return "Users{" +
                "id=" + id +
                ", userName='" + userName + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

1.4 dao层代码

package com.ljf.mybaits.relation.mapping.dao;

import com.ljf.mybaits.relation.mapping.domain.Orders;

import java.util.List;

public interface OrdersMapper {
    //查询全部的方法
    public List<Orders> findAll();
}

1.5 service层代码

1.service的接口

package com.ljf.mybaits.relation.mapping.service;

import com.ljf.mybaits.relation.mapping.domain.Orders;

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

public interface OrderService {
    public List<Orders> findAll() throws IOException;
}

2.service的实现层

package com.ljf.mybaits.relation.mapping.service.impl;

import com.ljf.mybaits.relation.mapping.dao.OrdersMapper;
import com.ljf.mybaits.relation.mapping.domain.Orders;
import com.ljf.mybaits.relation.mapping.service.OrderService;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;

/**
 * @ClassName: OrderServiceImpl
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/17 23:09:12 
 * @Version: V1.0
 **/
public class OrderServiceImpl implements OrderService {
    @Override
    public List<Orders> findAll() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("mybaitsConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrdersMapper mapper = sqlSession.getMapper(OrdersMapper.class);
        List<Orders> orderList = mapper.findAll();
        sqlSession.close();
        return orderList;
    }
}

1.6 resouces下的配置文件

1.log4j的配置


######################
## set log levels
######################
log4j.rootLogger=DEBUG,info,CONSOLE,FILEOUT
#DEBUG,CONSOLE,FILE,ROLLING_FILE,MAIL,DATABASE
log4j.addivity.org.apache=true
######################
## CONSOLE Appender ##
######################
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.Threshold=DEBUG
log4j.appender.CONSOLE.Target=System.out
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=[%-5p][%d{yyyy-MM-dd HH\:mm\:ss,SSS}][%c] \:%m%n
#log4j.appender.CONSOLE.layout.ConversionPattern=[framework] %d - %c -%-4r [%t] %-5p %c %x - %m%n\u00A0
#log4j.appender.CONSOLE.layout.ConversionPattern=[start]%d{DATE}[DATE]%n%p[PRIORITY]%n%x[NDC]%n%t[THREAD] n%c[CATEGORY]%n%m[MESSAGE]%n%n
######################
## Rolling File Appender
######################
log4j.appender.FILEOUT=org.apache.log4j.RollingFileAppender
log4j.appender.FILEOUT.File=E:/logs/allError.log
#log4j.appender.FILEOUT.Threshold=ALL
log4j.appender.FILEOUT.Threshold=INFO
log4j.appender.FILEOUT.Append=true
log4j.appender.fileout.MaxFileSize=1000KB
#log4j.appender.ROLLING_FILE.MaxBackupIndex=1
log4j.appender.FILEOUT.layout=org.apache.log4j.PatternLayout
log4j.appender.FILEOUT.layout.ConversionPattern=[%-5p][%d{yyyy-MM-dd HH\:mm\:ss,SSS}][%c] \:%m%n
#log4j.appender.CONSOLE.layout.ConversionPattern=[framework] %d - %c -%-4r [%t] %-5p %c %x - %m%n\u00A0
#######################
#info log
log4j.logger.info=info
log4j.appender.info=org.apache.log4j.DailyRollingFileAppender 
log4j.appender.info.DatePattern='_'yyyy-MM-dd'.log'
log4j.appender.info.File=d:/info.log
log4j.appender.info.Append=true
log4j.appender.info.Threshold=INFO
log4j.appender.info.layout=org.apache.log4j.PatternLayout 
log4j.appender.info.layout.ConversionPattern=[%-5p][%d{yyyy-MM-dd HH\:mm\:ss,SSS}][%c] \:%m%n
### File Appender
#######################
#log4j.appender.FILE=org.apache.log4j.FileAppender
#log4j.appender.FILE.File=E:/logs/all.log
#log4j.appender.FILE.Append=true
#log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
#log4j.appender.CONSOLE.layout.ConversionPattern=[%-5p][%d{yyyy-MM-dd HH\:mm\:ss,SSS}][%c] \:%m%n
##log4j.appender.CONSOLE.layout.ConversionPattern=[framework] %d - %c -%-4r [%t] %-5p %c %x - %m%n\u00A0
#####################
## Socket Appender
#####################
#log4j.appender.SOCKET=org.apache.log4j.RollingFileAppender
#log4j.appender.SOCKET.RemoteHost=localhost
#log4j.appender.SOCKET.Port=5001
#log4j.appender.SOCKET.LocationInfo=true
## Set up for Log Facter 5
#log4j.appender.SOCKET.layout=org.apache.log4j.PatternLayout
#log4j.appender.SOCET.layout.ConversionPattern=[start]%d{DATE}[DATE]%n%p[PRIORITY]%n%x[NDC]%n%t[THREAD]%n%c[CATEGORY]%n%m[MESSAGE]%n%n
#########################
## Log Factor 5 Appender
#########################
#log4j.appender.LF5_APPENDER=org.apache.log4j.lf5.LF5Appender
#log4j.appender.LF5_APPENDER.MaxNumberOfRecords=2000
########################
## SMTP Appender
########################
#log4j.appender.MAIL=org.apache.log4j.net.SMTPAppender
#log4j.appender.MAIL.Threshold=FATAL
#log4j.appender.MAIL.BufferSize=10
#[email protected]
#log4j.appender.MAIL.SMTPHost=mail.openwolf.com
#log4j.appender.MAIL.Subject=Log4J Message
#[email protected]
#log4j.appender.MAIL.layout=org.apache.log4j.PatternLayout
#log4j.appender.MAIL.layout.ConversionPattern=[framework] %d - %c -%-4r [%t] %-5p %c %x - %m%n
#########################
## JDBC Appender
########################
#log4j.appender.DATABASE=org.apache.log4j.jdbc.JDBCAppender
#log4j.appender.DATABASE.URL=jdbc:mysql://localhost:3306/test
#log4j.appender.DATABASE.driver=com.mysql.jdbc.Driver
#log4j.appender.DATABASE.user=root
#log4j.appender.DATABASE.password=root
#log4j.appender.DATABASE.sql=INSERT INTO LOG4J (Message) VALUES ('[framework] %d - %c -%-4r [%t] %-5p %c %x - %m%n')
#log4j.appender.DATABASE.layout=org.apache.log4j.PatternLayout
#log4j.appender.DATABASE.layout.ConversionPattern=[framework] %d - %c -%-4r [%t] %-5p %c %x - %m%n
#log4j.appender.A1=org.apache.log4j.DailyRollingFileAppender
#log4j.appender.A1.File=SampleMessages.log4j
#log4j.appender.A1.DatePattern=yyyyMMdd-HH'.log4j'
#log4j.appender.A1.layout=org.apache.log4j.xml.XMLLayout
####################
### myself Appender
####################
#log4j.appender.im = net.cybercorlin.util.logger.appender.IMAppender
#log4j.appender.im.host = mail.cybercorlin.net
#log4j.appender.im.username = username
#log4j.appender.im.password = password
#log4j.appender.im.recipient = [email protected]
#log4j.appender.im.layout=org.apache.log4j.PatternLayout
#log4j.appender.im.layout.ConversionPattern =[framework] %d - %c -%-4r [%t] %-5p %c %x - %m%n

2.jdbc.properties文件

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/nongda
jdbc.username=root
jdbc.password=

3.mybaitsConfig.xml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>
<properties resource="mybaits-jdbc.properties"></properties>
    <!-- 起别名-->
    <typeAliases>
        <typeAlias type="com.ljf.mybaits.relation.mapping.domain.Users" alias="user"></typeAlias>
        <typeAlias type="com.ljf.mybaits.relation.mapping.domain.Orders" alias="order"></typeAlias>
    </typeAliases>
    <!-- 注册类型注册器
    <typeHandlers>
        <typeHandler handler="com.mybaits.demo.handler.DataTypeTransfer"></typeHandler>
    </typeHandlers>
    -->
    <!--配置分页插件 -->
    <plugins>
        <plugin interceptor="com.github.pagehelper.PageHelper">
            <property name="dialect" value="mysql"/>
        </plugin>
    </plugins>
<!-- 数据源环境 -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <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>
 <!-- xxxmapper.xml都要在mybaits.config.xml文件中注册-->
    <mappers>
        <mapper resource="com/mybaits/mapper/OrderMapper.xml"></mapper>
    </mappers>

</configuration>

4.mapper.xml配置文件

1.orders.mapper文件：

<?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.ljf.mybaits.relation.mapping.dao.OrdersMapper">

    <resultMap id="orderMap" type="order">
        <!--手动指定字段与实体属性的映射关系
            column: 数据表的字段名称
            property：实体的属性名称
        -->
        <!--  -->
        <id column="oid" property="id"></id>
        <result column="order_time" property="orderTime"></result>
        <result column="total" property="total"></result>

        <!-- 方式一： user为Users实体中User类型的属性名  -->
        <result column="id" property="user.id"></result>
        <result column="user_name" property="user.userName"></result>
        <result column="password" property="user.password"></result>
        <result column="birthday" property="user.birthday"></result>

        <!--  方法二：
            property: 当前实体(order)中的属性名称(private User user)
            javaType: 当前实体(order)中的属性的类型(User)

        <association property="user" javaType="user">
            <id column="id" property="id"></id>
            <result column="user_name" property="userName"></result>
            <result column="password" property="password"></result>
            <result column="birthday" property="birthday"></result>
        </association>
-->
    </resultMap>

    <select id="findAll" resultMap="orderMap">
         SELECT o.id oid,o.order_time,o.total,u.id,u.user_name,u.birthday FROM tb_orders o,tb_users u WHERE o.uid=u.id
    </select>

</mapper>

1.7 执行结果：

package com.ljf.mybaits.relation.mapping;

import com.ljf.mybaits.relation.mapping.domain.Orders;
import com.ljf.mybaits.relation.mapping.service.OrderService;
import com.ljf.mybaits.relation.mapping.service.impl.OrderServiceImpl;

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

/**
 * Hello world!t
 *
 */
public class App 
{
    public static void main( String[] args ) throws IOException {
        OrderService os=new OrderServiceImpl();
        List<Orders> orderList=os.findAll();
        for (Orders order : orderList) {
            System.out.println(order);
        }
        System.out.println( "Hello World!" );
    }
}

二.1对n的关系

背景描述：用户表和订单表是1对n的关系，1个用户可以拥有多个订单。

2.1 userMapper配置文件

<?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="yonghuMapper">  -->
<mapper namespace="com.ljf.mybaits.relation.mapping.dao.UserMapper">
     <!-- 查询， 在mybaitsconfig.xml文件中给起了别名 -->
    <resultMap id="userMap" type="user">
        <id column="id" property="id"></id>
        <result column="user_name" property="userName"></result>
        <result column="password" property="password"></result>
        <result column="birthday" property="birthday"></result>
        <!--配置集合信息
            property:集合名称
            ofType：当前集合中的数据类型
        -->
        <collection property="orderList" ofType="order">
            <!--封装order的数据-->
            <id column="oid" property="id"></id>
            <result column="order_time" property="orderTime"></result>
            <result column="total" property="total"></result>
        </collection>
    </resultMap>

    <select id="findAll" resultMap="userMap">
           SELECT o.id oid,o.order_time,o.total,u.id,u.user_name,u.birthday FROM tb_orders o,tb_users u WHERE o.uid=u.id
    </select>



</mapper>

2.2 mybaitsconfig.xml配置文件

在此配置文件中添加此实体类的别名

2.3 dao层

package com.ljf.mybaits.relation.mapping.dao;



import com.ljf.mybaits.relation.mapping.domain.Users;

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

public interface UserMapper {
    List<Users> findAll() throws IOException;
}

2.4 service层

1.userservice代码

package com.ljf.mybaits.relation.mapping.service;

import com.ljf.mybaits.relation.mapping.domain.Orders;
import com.ljf.mybaits.relation.mapping.domain.Users;

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

public interface UserService {
    public List<Users> findAll() throws IOException;
}

2.userservice的实现层代码

package com.ljf.mybaits.relation.mapping.service.impl;

import com.ljf.mybaits.relation.mapping.dao.UserMapper;
import com.ljf.mybaits.relation.mapping.domain.Users;
import com.ljf.mybaits.relation.mapping.service.UserService;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;

/**
 * @ClassName: UserServiceImpl
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/18 13:29:09 
 * @Version: V1.0
 **/
public class UserServiceImpl implements UserService {
    @Override
    public List<Users> findAll() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("mybaitsConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<Users> userList = mapper.findAll();
        sqlSession.close();
        return userList;
    }
}

2.5 实体层

package com.ljf.mybaits.relation.mapping.domain;

import java.util.Date;
import java.util.List;

/**
 * @ClassName: Users
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/17 21:30:28 
 * @Version: V1.0
 **/
public class Users {
    private int id;
    private String userName;
    private Date birthday;
    //描述的是当前用户存在哪些订单
    private List<Orders> orderList;
    public int getId() {
        return id;
    }

    public void setId(int 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 List<Orders> getOrderList() {
        return orderList;
    }

    public void setOrderList(List<Orders> orderList) {
        this.orderList = orderList;
    }

    @Override
    public String toString() {
        return "Users{" +
                "id=" + id +
                ", userName='" + userName + '\'' +
                ", birthday=" + birthday +
                ", orderList=" + orderList +
                '}';
    }
}

2.6 调用

package com.ljf.mybaits.relation.mapping;

import com.ljf.mybaits.relation.mapping.domain.Users;
import com.ljf.mybaits.relation.mapping.service.UserService;
import com.ljf.mybaits.relation.mapping.service.impl.UserServiceImpl;

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

/**
 * @ClassName: APP2
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/18 13:18:28 
 * @Version: V1.0
 **/
public class APP2 {
    public static void main(String[] args) throws IOException {

        UserService us=new UserServiceImpl();
       List<Users> userList= us.findAll();
        for (Users user : userList) {
            System.out.println(user);
        }

    }
}

三.n对n的关系

背景描述：多对多的关系为：一个用户对应多个角色，用户和角色需要一张关系表来维护

3.1 数据库表设计

CREATE TABLE `tb_users` (
  `id` int(11) NOT NULL,
  `user_name` varchar(255) DEFAULT NULL,
  `birthday` datetime DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


CREATE TABLE `tb_user_role` (
  `uid` int(11) NOT NULL,
  `rid` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `tb_role` (
  `id` int(11) NOT NULL,
  `role_name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

3.2 实体bean的设计

package com.ljf.mybaits.relation.mapping.domain;

/**
 * @ClassName: Role
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/18 14:42:38 
 * @Version: V1.0
 **/
public class Role {
    private int id;
    private String roleName;

    public int getId() {
        return id;
    }

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

    public String getRoleName() {
        return roleName;
    }

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

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

user：

package com.ljf.mybaits.relation.mapping.domain;

import java.util.Date;
import java.util.List;

/**
 * @ClassName: Users
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/17 21:30:28 
 * @Version: V1.0
 **/
public class Users {
    private int id;
    private String userName;
    private Date birthday;
    //描述的是当前用户存在哪些订单
    private List<Orders> orderList;
    //描述的是当前用户具备哪些角色
    private List<Role> roleList;
    public int getId() {
        return id;
    }

    public void setId(int 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 List<Orders> getOrderList() {
        return orderList;
    }

    public void setOrderList(List<Orders> orderList) {
        this.orderList = orderList;
    }

    public List<Role> getRoleList() {
        return roleList;
    }

    public void setRoleList(List<Role> roleList) {
        this.roleList = roleList;
    }

    @Override
    public String toString() {
        return "Users{" +
                "id=" + id +
                ", userName='" + userName + '\'' +
                ", birthday=" + birthday +
                ", orderList=" + orderList +
                ", roleList=" + roleList +
                '}';
    }
}

3.3 userMapper配置文件

    <resultMap id="userRoleMap" type="user">
        <!--user的信息-->
        <id column="userId" property="id"></id>
        <result column="user_name" property="userName"></result>
        <result column="birthday" property="birthday"></result>
        <!--user内部的roleList信息  role是在mybaitsconfig.xml文件中给起了别名 -->
        <collection property="roleList" ofType="role">
            <id column="rid" property="id"></id>
            <result column="role_name" property="roleName"></result>
        </collection>
    </resultMap>

    <select id="findUserAndRoleAll" resultMap="userRoleMap">
        select a.id uid,a.user_name,a.birthday,b.uid,b.rid,c.id cid ,c.role_name from tb_users as a ,tb_user_role as b ,tb_role as c
        where a.id=b.uid and b.rid=c.id
    </select>

3.4 dao层

package com.ljf.mybaits.relation.mapping.dao;



import com.ljf.mybaits.relation.mapping.domain.Users;

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

public interface UserMapper {
    List<Users> findAll() throws IOException;
    public List<Users> findUserAndRoleAll();
}

3.5 service层

service接口

package com.ljf.mybaits.relation.mapping.service;

import com.ljf.mybaits.relation.mapping.domain.Orders;
import com.ljf.mybaits.relation.mapping.domain.Users;

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

public interface UserService {
    public List<Users> findAll() throws IOException;
    public List<Users> findUserAndRoleAll() throws IOException;
}

service的实现层

package com.ljf.mybaits.relation.mapping.service.impl;

import com.ljf.mybaits.relation.mapping.dao.UserMapper;
import com.ljf.mybaits.relation.mapping.domain.Users;
import com.ljf.mybaits.relation.mapping.service.UserService;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;

/**
 * @ClassName: UserServiceImpl
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/18 13:29:09 
 * @Version: V1.0
 **/
public class UserServiceImpl implements UserService {
    @Override
    public List<Users> findAll() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("mybaitsConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<Users> userList = mapper.findAll();
        sqlSession.close();
        return userList;
    }

    @Override
    public List<Users> findUserAndRoleAll() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("mybaitsConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<Users> userAndRoleAll = mapper.findUserAndRoleAll();
        sqlSession.close();
        return  userAndRoleAll;
    }
}

3.6 调用

package com.ljf.mybaits.relation.mapping;

import com.ljf.mybaits.relation.mapping.domain.Users;
import com.ljf.mybaits.relation.mapping.service.UserService;
import com.ljf.mybaits.relation.mapping.service.impl.UserServiceImpl;

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

/**
 * @ClassName: App3
 * @Description: TODO
 * @Author: liujianfu
 * @Date: 2021/02/18 14:50:15 
 * @Version: V1.0
 **/
public class App3 {
    public static void main(String[] args) throws IOException {
        UserService us=new UserServiceImpl();
       List<Users> userAndRoleAll =us.findUserAndRoleAll();
        for (Users user : userAndRoleAll) {
            System.out.println(user);
        }

    }
}

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