MyBatis的多表操作、基于xxxMapper.xml的一对一、一对多、多对多

1.一对一查询

2.一对多查询

3.多对多查询

4.代码

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>cn.itcast</groupId>
    <artifactId>Mybatis_day4_mutilquery</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <dependencies>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.32</version>
    </dependency>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.4.5</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>


    </dependencies>
    
</project>

jdbc.properties:

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

log4j.properties:

### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{
    
    ABSOLUTE} %5p %c{
    
    1}:%L - %m%n

### direct messages to file mylog.log ###
log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.File=c:/mylog.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{
    
    ABSOLUTE} %5p %c{
    
    1}:%L - %m%n

### set log levels - for more verbose logging change 'info' to 'debug' ###

log4j.rootLogger=debug, stdout

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>

    <!--通过properties标签加载外部properties文件-->
    <properties resource="jdbc.properties"></properties>
    
    <!--自定义别名-->
    <typeAliases>
        <typeAlias type="com.itheima.domain.Sys_user" alias="Sys_user"></typeAlias>
        <typeAlias type="com.itheima.domain.Order" alias="Order"></typeAlias>

    </typeAliases>


    <!--数据源环境-->
    <environments default="developement">
        <environment id="developement">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"></property>
                <property name="url" value="${jdbc.url}"></property>
                <property name="username" value="${jdbc.username}"></property>
                <property name="password" value="${jdbc.password}"></property>

            </dataSource>
        </environment>
    </environments>

    <!--加载映射文件-->
    <mappers>
        <mapper resource="com.itheima.mapper/UserMapper.xml"></mapper>
        <mapper resource="com.itheima.mapper/OrderMapper.xml"></mapper>

    </mappers>

    
</configuration>

上面的代码和上次写的差不多，主要看下面的
domain:

package com.itheima.domain;

import java.util.Date;

/**
 * @author QLBF
 * @version 1.0
 * @date 2021/2/1 16:32
 */
public class Order {
    
    
    private int id;
    private Date ordertime;
    private double total;

    //当前订单属于哪个用户（外键在实体类得用对象或者对象集合岚表示），1.演示一对一
    private Sys_user sys_user;

    @Override
    public String toString() {
    
    
        return "Order{" +
                "id=" + id +
                ", ordertime=" + ordertime +
                ", total=" + total +
                ", sys_user=" + sys_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 Sys_user getSys_user() {
    
    
        return sys_user;
    }

    public void setSys_user(Sys_user sys_user) {
    
    
        this.sys_user = sys_user;
    }
}

package com.itheima.domain;

import java.util.List;

/**
 * @author QLBF
 * @version 1.0
 * @date 2021/1/28 12:18
 */
public class Sys_user {
    
    
    private int id;
    private String username;
    private String email;
    private String password;
    private String phoneNum;

    //2.描述的是当前用户存在哪些订单，演示一对多
    private List<Order> orderList;

    //3.描述的是当前用户具备哪些角色，演示多对多
    private List<Role> roleList;

    @Override
    public String toString() {
    
    
        return "Sys_user{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", email='" + email + '\'' +
                ", password='" + password + '\'' +
                ", phoneNum='" + phoneNum + '\'' +
                ", orderList=" + orderList +
                ", roleList=" + roleList +
                '}';
    }

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

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

    public List<Order> getOrderList() {
    
    
        return orderList;
    }

    public void setOrderList(List<Order> orderList) {
    
    
        this.orderList = 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 String getEmail() {
    
    
        return email;
    }

    public void setEmail(String email) {
    
    
        this.email = email;
    }

    public String getPassword() {
    
    
        return password;
    }

    public void setPassword(String password) {
    
    
        this.password = password;
    }

    public String getPhoneNum() {
    
    
        return phoneNum;
    }

    public void setPhoneNum(String phoneNum) {
    
    
        this.phoneNum = phoneNum;
    }
}

package com.itheima.domain;

/**
 * @author QLBF
 * @version 1.0
 * @date 2021/2/1 18:22
 */
public class Role {
    
    
    private int id;
    private String roleName;
    private String roleDesc;

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

    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;
    }

    public String getRoleDesc() {
    
    
        return roleDesc;
    }

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

mapper:

package com.itheima.mapper;

import com.itheima.domain.Order;

import java.util.List;

/**
 * @author QLBF
 * @version 1.0
 * @date 2021/2/1 16:37
 */
public interface OrderMapper {
    
    

    public List<Order> findAll();  //演示一对一，一个订单对应一个用户，全部查出来而已

}

package com.itheima.mapper;

import com.itheima.domain.Role;
import com.itheima.domain.Sys_user;

import java.util.List;

/**
 * @author QLBF
 * @version 1.0
 * @date 2021/1/30 11:06
 */
public interface UserMapper {
    
    

    public List<Sys_user> findAlluser_duodingdan();//2.演示一对多，一个用户有多个订单

    public List<Sys_user> findUserAndRoleAll();//3.演示多对多，一个用户有多个角色，一个角色哟多个用户
}

4.1映射文件（重点）

com.itheima.mapper/OrderMapper.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.itheima.mapper.OrderMapper">
    <!--1.#####################################################-->
    <!--演示一对一，一个订单对应一个用户，全部查出来而已-->
    <!--Order是在核心配置文件的别名-->
    <resultMap id="orderMap" type="Order">
        <!--手动指定数据表字段与实体属性的映射关系
        column:你用语句查出来的数据表的字段名称(还是看你写的sql，查询的sql查出来的字段名（别名也可以），column还可以用你查出来的别名 )
        property：实体的属性名称-->
        <id column="oid" property="id"></id>
        <result column="ordertime" property="ordertime"></result>
        <result column="total" property="total"></result>

        <!--property:是当前实体(Order)中的属性名称(private Sys_user sys_user)
        javaType:当前实体（Order）中的属性的类型（Sys_user类型，这里要写全包名的，但Sys_user是我定义的别名啦）-->
        <association property="sys_user" javaType="Sys_user">
            <!--这里虽然写sys_user的类型，但是property还是写当前实体的uid(就是写你查询的sql查出来的字段名（别名也可以），如不是写Sys_user的字段名哦-->
            <id column="uid" property="id"></id>
            <result column="username" property="username"></result>
            <result column="email" property="email"></result>
            <result column="password" property="password"></result>
            <result column="phoneNum" property="phoneNum"></result>
        </association>
    </resultMap>

    <select id="findAll" resultMap="orderMap">
--         定义查o.id oid好区分两个相同的id而已
        SELECT *,o.id oid FROM orders o,sys_user u WHERE o.uid=u.`id`
    </select>





</mapper>

com.itheima.mapper/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="com.itheima.mapper.UserMapper">
    <!--2.演示一对多，一个用户多个订单-->
    <resultMap id="userMap" type="Sys_user">
        <id column="uid" property="id"></id>
        <result column="username" property="username"></result>
        <result column="email" property="email"></result>
        <result column="password" property="password"></result>
        <result column="phoneNum" property="phoneNum"></result>
        <!--配置集合信息，之前一对一是配置association，这里是collection
            property：还是实体的集合名称（对应Sys_user的private List<Order> orderList;）
            ofType：当前集合中的数据类型，为sqlMapConfig的别名Order-->
        <collection property="orderList" ofType="Order">
            <!--封装order的数据-->
            <id column="oid" property="id"></id>
            <result column="ordertime" property="ordertime"></result>
            <result column="total" property="total"></result>
        </collection>
    </resultMap>

    <select id="findAlluser_duodingdan" resultMap="userMap">
        SELECT *,o.`id` oid FROM sys_user u,orders o WHERE u.`id`=o.`uid`
    </select>


    <!--##########################################################################-->

    <!--3.演示多对多，一个用户有多个角色，一个角色哟多个用户-->
    <resultMap id="userRoleMap" type="Sys_user">
        <id column="userId" property="id"></id>
        <result column="username" property="username"></result>
        <result column="email" property="email"></result>
        <result column="password" property="password"></result>
        <result column="phoneNum" property="phoneNum"></result>

        <!--Sys_user的roleList信息,这里ofType不使用别名了，你可以在sqlMapConfig设置role的别名也可以-->
        <collection property="roleList" ofType="com.itheima.domain.Role">
            <id column="roleId" property="id"></id>
            <result column="roleName" property="roleName"></result>
            <result column="roleDesc" property="roleDesc"></result>
        </collection>
    </resultMap>
    <select id="findUserAndRoleAll" resultMap="userRoleMap">
        SELECT *FROM sys_user u,sys_user_role ur,sys_role r WHERE u.`id`=ur.`userId` AND r.`id`=ur.`roleId`
    </select>
</mapper>

com.itheima.service.ServiceDemo测试代码：

package com.itheima.service;


import com.itheima.domain.Order;
import com.itheima.domain.Sys_user;
import com.itheima.mapper.OrderMapper;
import com.itheima.mapper.UserMapper;
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.Test;

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

/**
 * @author QLBF
 * @version 1.0
 * @date 2021/1/30 11:07
 */
public class ServiceDemo {
    
    

    @Test
    //1.演示一对一，一个订单对应一个用户，全部查出来而已
    public void test1() throws IOException {
    
    

        InputStream resourceAsStream= Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession=sqlSessionFactory.openSession(true);

        OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
        List<Order> orderList = mapper.findAll();
        for (Order order : orderList) {
    
    
            System.out.println(order);
        }

    }

    @Test
    //2.演示一对多，一个用户对应多个订单
    public void test2() throws IOException {
    
    

        InputStream resourceAsStream= Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession=sqlSessionFactory.openSession(true);

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<Sys_user> sys_userList = mapper.findAlluser_duodingdan();
        for (Sys_user sys_user : sys_userList) {
    
    
            System.out.println(sys_user);
        }

    }


    @Test
    //3.演示多对多，一个用户有多个角色，一个角色哟多个用户
    public void test3() throws IOException {
    
    

        InputStream resourceAsStream= Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession=sqlSessionFactory.openSession(true);

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<Sys_user> sys_userList = mapper.findUserAndRoleAll();
        for (Sys_user sys_user : sys_userList) {
    
    
            System.out.println(sys_user);
        }

    }
}

5.总结

一对多：那么就要在一的实体类定义对象集合（多），多对多就随便在一个定义另一个的集合对象

之前在xxMapper.xml是写resultType的，现在要写resultMap了，且resultMap要自己在xml写。

在xxxMapper.xml中的resultMap配：
id代表int，
result一般代表varchar、double等
association代表一个对象
collection代表对象集合类型

column:你用语句查出来的数据表的字段名称(还是看你写的sql，查询的sql查出来的字段名（别名也可以），column还可以用你查出来的别名 )
property：实体的属性名称

下面图片是xxxMapper.xml的：