MyBatis（XML映射器操作）

发布于：2024-05-05 ⋅ 阅读:(23) ⋅ 点赞:(0)

文章目录

XML映射器操作（XxxMapper.xml）

文件目录

image-20240304162123528

1.基本介绍
1.优点

image-20240304102427876

2.常用顶级元素

image-20240304102444648

2.环境配置
1.在原来的父模块下创建一个子模块

image-20240304103035583

2.删除没用的两个文件夹

image-20240304103249466

3.创建基本目录

image-20240304104018475

4.父模块的pom.xml
<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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.example</groupId>
  <artifactId>mybatis</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>pom</packaging>
  <name>Archetype - mybatis</name>
  <url>http://maven.apache.org</url>
  <modules>
    <module>mybatis_quickstart</module>
    <module>xml-mapper</module>
  </modules>
  <dependencies>
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.49</version>
    </dependency>
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.5.7</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <!--如果设置scope为test,则只能在test包下使用-->
      <scope>test</scope>
    </dependency>
  </dependencies>
  <!--在父模块中的pom.xml文件中配置在build的时候要扫描的文件，解决某些类型文件拷贝到target目录失败的问题-->
  <build>
    <resources>
      <resource>
        <directory>src/main/java</directory>
        <includes>
          <!--在java文件夹下的多级目录下的xml文件-->
          <include>**/*.xml</include>
        </includes>
      </resource>
      <resource>
        <directory>src/main/resources</directory>
        <includes>
          <!--在resources文件夹下的多级目录下的xml文件和properties文件-->
          <include>**/*.xml</include>
          <include>**/*.properties</include>
        </includes>
      </resource>
    </resources>
  </build>
</project>
5.jdbc.properties
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/mybatis?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8
jdbc.username=root
jdbc.password=root
6.mybatis-config.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!--引入外部文件jdbc.properties-->
    <properties resource="jdbc.properties"/>

    <!--配置mybatis自带的日志，settings需要放到最前面-->
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>

    <!--配置类型别名-->
    <typeAliases>
        <!--方式二：这样配置完了在这个包下的所有类都可以直接使用类名表示-->
        <package name="com.sun.entity"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <!--配置事务管理器-->
            <transactionManager type="JDBC"/>
            <!--配置数据源-->
            <dataSource type="POOLED">
                <!--配置驱动-->
                <property name="driver" value="${jdbc.driver}"/>
                <!--配置连接url-->
                <!--
                1.jdbc:mysql：协议
                2.127.0.0.1:3306：指定连接mysql的ip+端口
                3.mybatis：连接的db
                4.useSSL：使用安全连接
                5.&amp;：表示&
                6.useUnicode=true：使用unicode,防止编码错误
                7.characterEncoding=UTF-8：字符集使用utf-8
                -->
                <property name="url" value="${jdbc.url}"/>
                <!--用户名-->
                <property name="username" value="${jdbc.username}"/>
                <!--密码-->
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <!--包的方式引入含有Mapper.xml的类-->
        <package name="com.sun.mapper"/>
    </mappers>

</configuration>
7.测试使用MonsterMapperTest.java
package com.sun.mapper;

import com.util.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Before;
import org.junit.Test;

/**
 * @author 孙显圣
 * @version 1.0
 */
public class MonsterMapperTest {
    //两个属性
    private SqlSession sqlSession; //相当于连接
    private MonsterMapper monsterMapper;

    //编写方法完成初始化
    @Before //标注了Before之后表示了在执行目标测试方法前会执行该方法
    public void init() {
        //获取到sqlSession
        sqlSession = MyBatisUtils.getSqlSession();
        //获取到MonsterMapper对象
        monsterMapper = sqlSession.getMapper(MonsterMapper.class);
        System.out.println(monsterMapper.getClass());
    }
    @Test
    public void test() {
        System.out.println("ssss");
    }
}

image-20240304105411141

3.parameterType（输入参数类型）
1.基本介绍

image-20240304105809901

2.案例一
1.MonsterMapper.java
package com.sun.mapper;


import com.sun.entity.Monster;

import java.util.List;

/**
 * 这个接口用于声明操作monster表的方法
 *
 * @author 孙显圣
 * @version 1.0
 */
public interface MonsterMapper {
    //通过id或者名字查询
    public List<Monster> findMonsterByNameORId(Monster monster);

}
2.MonsterMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--指定该xml文件和哪个接口对应-->
<mapper namespace="com.sun.mapper.MonsterMapper">
    <!--实现public List<Monster> findMonsterByNameORId(Monster monster);
	这里能直接写Monster是因为配置文件里配置了类型别名
	-->
    <select id="findMonsterByNameORId" parameterType="Monster" resultType="Monster">
        SELECT * FROM monster WHERE id = #{id} OR `name` = #{name}
    </select>
</mapper>
3.测试
package com.sun.mapper;

import com.sun.entity.Monster;
import com.util.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Before;
import org.junit.Test;

import java.util.List;

/**
 * @author 孙显圣
 * @version 1.0
 */
public class MonsterMapperTest {
    //两个属性
    private SqlSession sqlSession; //相当于连接
    private MonsterMapper monsterMapper;

    //编写方法完成初始化
    @Before //标注了Before之后表示了在执行目标测试方法前会执行该方法
    public void init() {
        //获取到sqlSession
        sqlSession = MyBatisUtils.getSqlSession();
        //获取到MonsterMapper对象
        monsterMapper = sqlSession.getMapper(MonsterMapper.class);
        System.out.println(monsterMapper.getClass());
    }
    @Test
    public void test() {
        Monster monster = new Monster();
        monster.setId(1);
        monster.setName("大象精");
        List<Monster> monsterList = monsterMapper.findMonsterByNameORId(monster);
        for (Monster monster1 : monsterList) {
            System.out.println(monster1);
        }
        //关闭sqlsession
        if (sqlSession != null) {
            sqlSession.close();
        }
    }
}

image-20240304111611381

3.案例二（模糊查询）
1.MonsterMapper.java添加方法
    public List<Monster> findMonsterByName(String name);
2.MonsterMapper.xml添加实现类
    <!--实现public List<Monster> findMonsterByName(String name);-->
    <select id="findMonsterByName" parameterType="String" resultType="Monster">
        SELECT * FROM monster WHERE `name` LIKE '%${name}%'
    </select>
3.测试
    @Test
    public void MonsterMapper() {
        List<Monster> monsterList = monsterMapper.findMonsterByName("孙");
        for (Monster monster : monsterList) {
            System.out.println(monster);
        }
    }

image-20240304134750221

4.传入HashMap
1.基本介绍image-20240304135016653
2.案例一（参数为map）
1.MonsterMapper.java添加方法
    //传入map
    public List<Monster> findMonsterByIdAndName_ParamMap(Map<String, Object> map);
2.MonsterMapper.xml
    <!--这里如果想要获取到id和name则需要这个Map里面有这两个key-->
    <select id="findMonsterByIdAndName_ParamMap" parameterType="Map" resultType="Monster">
        SELECT * FROM monster WHERE id = #{id} OR `name` = #{name}
    </select>
3.测试
    @Test
    public void findMonsterByIdAndName_ParamMap() {
        Map map = new HashMap<String, Object>();
        map.put("id", 1);
        map.put("name", "大象精");
        List<Monster> monsters = monsterMapper.findMonsterByIdAndName_ParamMap(map);
        for (Monster monster : monsters) {
            System.out.println(monster);
        }
    }

image-20240304140423827

3.案例二（返回值为map）
1.MonsterMapper.java添加方法
    //以map作为返回参数
    public List<Map<String, Object>> findMonsterByIdAndName_ParamMap_returnMap(Map<String, Object> map);
2.MonsterMapper.xml
    <!--返回值是List，每一个元素都是一个map，而一个map代表了一条记录，key代表列，value代表值-->
    <select id="findMonsterByIdAndName_ParamMap_returnMap" parameterType="Map" resultType="Map">
        SELECT * FROM monster WHERE id = #{id} OR `name` = #{name}
    </select>
3.测试
    @Test
    public void findMonsterByIdAndName_ParamMap_returnMap() {
        Map map = new HashMap<String, Object>();
        map.put("id", 6);
        map.put("name", "大象精");
        List<Map<String, Object>> mapList = monsterMapper.findMonsterByIdAndName_ParamMap_returnMap(map);
        //取出所有map
        for (Map<String, Object> stringObjectMap : mapList) {
            for (Map.Entry<String, Object> entry : stringObjectMap.entrySet()) {
                System.out.println(entry.getKey() + " " + entry.getValue());
            }
        }
    }

image-20240304142058962

5.ResultMap
1.基本介绍

image-20240304142524912

2.案例
1.创建数据表
CREATE TABLE `user` (
	user_id INT NOT NULL auto_increment,
	user_email VARCHAR(255) DEFAULT '',
	user_name VARCHAR(255) DEFAULT'',
	PRIMARY KEY (user_id)
)
2.创建映射类User.java
package com.sun.entity;


/**
 * @author 孙显圣
 * @version 1.0
 */

public class User {
    private Integer user_id;
    //下面两个字段与数据表的字段不对应
    private String username; 
    private String useremail;

    public User() {
    }

    public User(Integer user_id, String username, String useremail) {
        this.user_id = user_id;
        this.username = username;
        this.useremail = useremail;
    }

    public Integer getUser_id() {
        return user_id;
    }

    public void setUser_id(Integer user_id) {
        this.user_id = user_id;
    }

    public String getUsername() {
        return username;
    }

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

    public String getUseremail() {
        return useremail;
    }

    public void setUseremail(String useremail) {
        this.useremail = useremail;
    }

    @Override
    public String toString() {
        return "User{" +
                "user_id=" + user_id +
                ", username='" + username + '\'' +
                ", useremail='" + useremail + '\'' +
                '}';
    }
}
3.UserMapper.java
UserMapper.xmlpackage com.sun.mapper;

import com.sun.entity.User;

import java.util.List;

/**
 * @author 孙显圣
 * @version 1.0
 */
public interface UserMapper {
    //查询所有UserMapper.xmlser
    public List<User> findAllUser();
}
4.UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--指定该xml文件和哪个接口对应-->
<mapper namespace="com.sun.mapper.UserMapper">
    <select id="findAllUser" resultType="User">
        SELECT * FROM user
    </select>
</mapper>
5.测试（数据未填充！）
package com.sun.mapper;

import com.sun.entity.User;
import com.util.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Before;
import org.junit.Test;

import java.util.List;

/**
 * @author 孙显圣
 * @version 1.0
 */
public class UserMapperTest {
    //两个属性
    private SqlSession sqlSession; //相当于连接
    private UserMapper userMapper;

    //编写方法完成初始化
    @Before //标注了Before之后表示了在执行目标测试方法前会执行该方法
    public void init() {
        //获取到sqlSession
        sqlSession = MyBatisUtils.getSqlSession();
        //获取到MonsterMapper对象
        userMapper = sqlSession.getMapper(UserMapper.class);
        System.out.println(userMapper.getClass());
    }

    @Test
    public void findAllUser() {
        List<User> allUser = userMapper.findAllUser();
        System.out.println(allUser);
    }
}

image-20240304145105755

6.使用resultMap替换resultType解决，修改UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--指定该xml文件和哪个接口对应-->
<mapper namespace="com.sun.mapper.UserMapper">
    <!--使用resultMap替换resultType，来进行映射类的属性与表之间的映射-->
    <resultMap id="findAllUserResultType" type="User">
        <result column="user_email" property="useremail"/>
        <result column="user_name" property="username"/>
    </resultMap>
    <select id="findAllUser" resultMap="findAllUserResultType">
        SELECT * FROM user
    </select>
</mapper>
7.结果

image-20240304155238444

3.注意事项与细节
  • 如果没有使用resultMap，但是表的列名与映射类的属性不匹配，则返回的结果不会填充，则该位置会是对象属性的默认值
  • 解决列名与属性名不同也可以使用别名，简单来说就是查询出来结果的时候使用as，将结果所在的列名设置成跟属性一致的名字，但是不推荐
  • MyBatis-Plus可以直接使用@TableField注解或者@TableName注解来解决

image-20240304155904444

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