目录

1.依赖

2.示例代码

2.1不带resultMap标签示例

2.1带resultMap标签示例

3.resultMap标签不加的情况说明

---

1.依赖

在pom.xml文件中引入依赖

      <dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter-test</artifactId><version>3.0.3</version><scope>test</scope></dependency>

2.示例代码

提示：在resource下创建文件mapper，用于存放xml配置文件

2.1不带resultMap标签示例

dao接口：

package com.example.springbootdemo.Mapper;import com.example.springbootdemo.pojo.Student;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select;import java.time.LocalDate;
import java.util.List;@Mapper
public interface StudentMapper{@Insert("insert into td_student(username, password, name, gender, age,create_time, update_time) "+"values(#{username},#{password},#{name},#{gender},#{age},#{createTime},#{updateTime})")void insert(Student student);void delete(List<Integer> ids);void update(Student student);List<Student> list(String name, Short gender, LocalDate begin, LocalDate end);@Select("select * from td_student where  id = #{id}")Student getById(Integer id);@Select("select * from td_student where username=#{username}")Student getByUserName(String username);
}

对应的xml映射文件：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.springbootdemo.Mapper.StudentMapper"><update id="update">update td_student<set><if test="username != null and username != ''">username = #{username},</if><if test="password != null and password != ''">password = #{password},</if><if test="gender != null">gender = #{gender},</if><if test="age != null">age = #{age},</if><if test="name != null and name != ''">name = #{name},</if><if test="updateTime != null">update_time = #{updateTime},</if></set>where id = #{id}</update><delete id="delete">delete from td_student where id in<foreach collection="ids" item="id" separator="," open="(" close=")">#{id}</foreach></delete><select id="list" resultType="com.example.springbootdemo.pojo.Student">select * from td_student<where><if test="name != null and name != ''">name like concat('%',#{name},'%')</if><if test="gender != null">and gender = #{gender}</if><if test="begin != null and end != null">and entrydate = between #{begin} and #{end}</if></where>order by update_time desc</select></mapper>

当然还有这种加resultMap标签的情况：

2.1带resultMap标签示例

<?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.example.dao.UserDao">  <!-- 定义User的结果映射 -->  <resultMap id="UserResultMap" type="com.example.model.User">  <id property="id" column="id" />  <result property="name" column="name" />  <result property="email" column="email" />  </resultMap>  <!-- 插入用户 -->  <insert id="insertUser" parameterType="com.example.model.User">  INSERT INTO user (name, email) VALUES (#{name}, #{email})  </insert>  <!-- 根据ID查询用户 -->  <select id="getUserById" parameterType="java.lang.Integer" resultType="com.example.model.User">  SELECT * FROM user WHERE id = #{id}  </select>  <!-- 查询所有用户 -->  <select id="getAllUsers" resultMap="UserResultMap">  SELECT * FROM user  </select>  <!-- 更新用户 -->  <update id="updateUser" parameterType="com.example.model.User">  UPDATE user SET name = #{name}, email = #{email} WHERE id = #{id}  </update>  <!-- 删除用户 -->  <delete id="deleteUser" parameterType="java.lang.Integer">  DELETE FROM user WHERE id = #{id}  </delete>  </mapper>

3.resultMap标签不加的情况说明

这取决于你的具体需求。<resultMap> 在 MyBatis 中主要用于处理复杂的映射情况，比如联合查询、嵌套结果等。对于简单的 CRUD 操作，如果不涉及复杂的映射关系，通常不需要显式定义 <resultMap>。

对于你的 User 实体类，如果它的属性名和数据库表中的列名完全一致，并且你不做特殊的映射处理（比如将数据库中的某个列映射到 Java 对象的另一个属性），那么你可以直接使用 resultType 来指定返回结果的类型，而不需要定义 <resultMap>。

resultType 告诉 MyBatis 返回的结果应该被映射到 com.example.model.User 类型的对象上。MyBatis 会根据 SQL 查询返回的列名自动匹配 User 类中的属性名，并将相应的值赋给属性。

然而，如果你需要处理更复杂的场景，比如列名和属性名不匹配，或者需要映射到嵌套的对象，那么你就需要定义 <resultMap> 来进行详细的映射配置。