MyBatis基础操作完整指南

MyBatis简介

MyBatis是Apache的一个开源项目，前身是iBatis。它是一个基于Java的持久层框架，主要特点包括：相比Hibernate等ORM框架，MyBatis更加轻量级，并且支持自定义SQL，能够充分利用数据库特性。

环境搭建

Maven依赖

首先在pom.xml中添加MyBatis相关依赖：

<dependencies><!-- MyBatis核心依赖 --><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.13</version></dependency><!-- MySQL驱动 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.33</version></dependency>
</dependencies>

数据库表结构

创建一个用户表：

CREATE TABLE `user` (`id` int(11) NOT NULL AUTO_INCREMENT,`username` varchar(50) NOT NULL,`email` varchar(100) DEFAULT NULL,`age` int(3) DEFAULT NULL,`created_time` datetime DEFAULT CURRENT_TIMESTAMP,PRIMARY KEY (`id`)
);

核心配置

MyBatis配置文件

创建mybatis-config.xml核心配置文件：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><!-- 属性配置 --><properties resource="database.properties"/><!-- 设置 --><settings><!-- 开启驼峰命名自动映射 --><setting name="mapUnderscoreToCamelCase" value="true"/></settings><!-- 类型别名 --><typeAliases><package name="com.example.entity"/></typeAliases><!-- 环境配置 --><environments default="development"><environment id="development"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="${database.driver}"/><property name="url" value="${database.url}"/><property name="username" value="${database.username}"/><property name="password" value="${database.password}"/></dataSource></environment></environments><!-- 映射器配置 --><mappers><mapper resource="mapper/UserMapper.xml"/></mappers>
</configuration>

数据库配置文件

创建database.properties文件：

database.driver=com.mysql.cj.jdbc.Driver
database.url=jdbc:mysql://localhost:3306/mybatis
database.username=root
database.password=123456

实体类

创建User实体类：

package com.example.entity;import java.time.LocalDateTime;public class User {private Integer id;private String username;private String email;private Integer age;private LocalDateTime createdTime;// 构造方法public User() {}public User(String username, String email, Integer age) {this.username = username;this.email = email;this.age = age;}// getter和setter方法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 String getEmail() {return email;}public void setEmail(String email) {this.email = email;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public LocalDateTime getCreatedTime() {return createdTime;}public void setCreatedTime(LocalDateTime createdTime) {this.createdTime = createdTime;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", email='" + email + '\'' +", age=" + age +", createdTime=" + createdTime +'}';}
}

基础CRUD操作

Mapper接口

创建UserMapper接口：

package com.example.mapper;import com.example.entity.User;
import java.util.List;public interface UserMapper {// 插入用户int insertUser(User user);// 根据ID删除用户int deleteUserById(Integer id);// 更新用户信息int updateUser(User user);// 根据ID查询用户User selectUserById(Integer id);// 查询所有用户List<User> selectAllUsers();// 根据用户名查询用户List<User> selectUsersByUsername(String username);
}

Mapper XML映射文件

创建UserMapper.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.mapper.UserMapper"><!-- 结果映射 --><resultMap id="userResultMap" type="User"><id property="id" column="id"/><result property="username" column="username"/><result property="email" column="email"/><result property="age" column="age"/><result property="createdTime" column="created_time"/></resultMap><!-- 插入用户 --><insert id="insertUser" parameterType="User" useGeneratedKeys="true" keyProperty="id">INSERT INTO user (username, email, age)VALUES (#{username}, #{email}, #{age})</insert><!-- 根据ID删除用户 --><delete id="deleteUserById" parameterType="int">DELETE FROM user WHERE id = #{id}</delete><!-- 更新用户信息 --><update id="updateUser" parameterType="User">UPDATE user SETusername = #{username},email = #{email},age = #{age}WHERE id = #{id}</update><!-- 根据ID查询用户 --><select id="selectUserById" parameterType="int" resultMap="userResultMap">SELECT id, username, email, age, created_timeFROM userWHERE id = #{id}</select><!-- 查询所有用户 --><select id="selectAllUsers" resultMap="userResultMap">SELECT id, username, email, age, created_timeFROM userORDER BY created_time DESC</select><!-- 根据用户名查询用户 --><select id="selectUsersByUsername" parameterType="string" resultMap="userResultMap">SELECT id, username, email, age, created_timeFROM userWHERE username LIKE CONCAT('%', #{username}, '%')</select></mapper>

工具类

创建MyBatis工具类：

package com.example.util;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;public class MyBatisUtil {private static SqlSessionFactory sqlSessionFactory;static {try {// 读取配置文件InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");// 创建SqlSessionFactorysqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);} catch (IOException e) {e.printStackTrace();}}// 获取SqlSessionpublic static SqlSession getSqlSession() {return sqlSessionFactory.openSession();}// 获取自动提交的SqlSessionpublic static SqlSession getSqlSession(boolean autoCommit) {return sqlSessionFactory.openSession(autoCommit);}
}

测试类

创建测试类验证CRUD操作：

package com.example.test;import com.example.entity.User;
import com.example.mapper.UserMapper;
import com.example.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;import java.util.List;public class MyBatisTest {public static void main(String[] args) {// 测试插入testInsert();// 测试查询testSelect();// 测试更新testUpdate();// 测试删除testDelete();}// 测试插入public static void testInsert() {SqlSession sqlSession = MyBatisUtil.getSqlSession();try {UserMapper mapper = sqlSession.getMapper(UserMapper.class);User user = new User("张三", "[e-mail]", 25);int result = mapper.insertUser(user);sqlSession.commit();System.out.println("插入结果: " + result + ", 用户ID: " + user.getId());} finally {sqlSession.close();}}// 测试查询public static void testSelect() {SqlSession sqlSession = MyBatisUtil.getSqlSession();try {UserMapper mapper = sqlSession.getMapper(UserMapper.class);// 查询所有用户List<User> users = mapper.selectAllUsers();System.out.println("所有用户: " + users);// 根据ID查询if (!users.isEmpty()) {User user = mapper.selectUserById(users.get(0).getId());System.out.println("根据ID查询: " + user);}} finally {sqlSession.close();}}// 测试更新public static void testUpdate() {SqlSession sqlSession = MyBatisUtil.getSqlSession();try {UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> users = mapper.selectAllUsers();if (!users.isEmpty()) {User user = users.get(0);user.setAge(30);user.setEmail("[e-mail]");int result = mapper.updateUser(user);sqlSession.commit();System.out.println("更新结果: " + result);}} finally {sqlSession.close();}}// 测试删除public static void testDelete() {SqlSession sqlSession = MyBatisUtil.getSqlSession();try {UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> users = mapper.selectAllUsers();if (!users.isEmpty()) {int result = mapper.deleteUserById(users.get(0).getId());sqlSession.commit();System.out.println("删除结果: " + result);}} finally {sqlSession.close();}}
}

动态SQL

MyBatis提供了强大的动态SQL功能，可以根据条件动态生成SQL语句：

常用标签

<!-- if标签：条件判断 -->
<select id="selectUsersByCondition" parameterType="User" resultMap="userResultMap">SELECT * FROM userWHERE 1=1<if test="username != null and username != ''">AND username LIKE CONCAT('%', #{username}, '%')</if><if test="email != null and email != ''">AND email = #{email}</if><if test="age != null">AND age = #{age}</if>
</select><!-- where标签：智能处理WHERE关键字和AND/OR -->
<select id="selectUsersWithWhere" parameterType="User" resultMap="userResultMap">SELECT * FROM user<where><if test="username != null and username != ''">username LIKE CONCAT('%', #{username}, '%')</if><if test="email != null and email != ''">AND email = #{email}</if><if test="age != null">AND age = #{age}</if></where>
</select><!-- choose、when、otherwise：类似switch语句 -->
<select id="selectUsersByChoose" parameterType="User" resultMap="userResultMap">SELECT * FROM user<where><choose><when test="username != null and username != ''">username LIKE CONCAT('%', #{username}, '%')</when><when test="email != null and email != ''">email = #{email}</when><otherwise>age &gt; 18</otherwise></choose></where>
</select><!-- set标签：用于UPDATE语句 -->
<update id="updateUserSelective" parameterType="User">UPDATE user<set><if test="username != null and username != ''">username = #{username},</if><if test="email != null and email != ''">email = #{email},</if><if test="age != null">age = #{age}</if></set>WHERE id = #{id}
</update><!-- foreach标签：循环处理集合 -->
<select id="selectUsersByIds" parameterType="list" resultMap="userResultMap">SELECT * FROM userWHERE id IN<foreach collection="list" item="id" open="(" separator="," close=")">#{id}</foreach>
</select>

高级特性

一对一关联映射

<!-- 用户订单一对一关系 -->
<resultMap id="userWithOrderResultMap" type="User"><id property="id" column="user_id"/><result property="username" column="username"/><association property="order" javaType="Order"><id property="id" column="order_id"/><result property="orderNo" column="order_no"/><result property="amount" column="amount"/></association>
</resultMap><select id="selectUserWithOrder" resultMap="userWithOrderResultMap">SELECT u.id as user_id, u.username, o.id as order_id, o.order_no, o.amountFROM user uLEFT JOIN order o ON u.id = o.user_idWHERE u.id = #{id}
</select>

一对多关联映射

<!-- 用户订单一对多关系 -->
<resultMap id="userWithOrdersResultMap" type="User"><id property="id" column="user_id"/><result property="username" column="username"/><collection property="orders" ofType="Order"><id property="id" column="order_id"/><result property="orderNo" column="order_no"/><result property="amount" column="amount"/></collection>
</resultMap><select id="selectUserWithOrders" resultMap="userWithOrdersResultMap">SELECT u.id as user_id, u.username,o.id as order_id, o.order_no, o.amountFROM user uLEFT JOIN order o ON u.id = o.user_idWHERE u.id = #{id}
</select>

分页查询

<!-- 分页查询 -->
<select id="selectUsersWithPage" parameterType="map" resultMap="userResultMap">SELECT * FROM userORDER BY created_time DESCLIMIT #{offset}, #{pageSize}
</select><!-- 查询总数 -->
<select id="countUsers" resultType="int">SELECT COUNT(*) FROM user
</select>

使用注解方式

public interface UserMapper {@Insert("INSERT INTO user (username, email, age) VALUES (#{username}, #{email}, #{age})")@Options(useGeneratedKeys = true, keyProperty = "id")int insertUserWithAnnotation(User user);@Delete("DELETE FROM user WHERE id = #{id}")int deleteUserByIdWithAnnotation(@Param("id") Integer id);@Update("UPDATE user SET username = #{username}, email = #{email}, age = #{age} WHERE id = #{id}")int updateUserWithAnnotation(User user);@Select("SELECT * FROM user WHERE id = #{id}")@Results({@Result(property = "id", column = "id"),@Result(property = "username", column = "username"),@Result(property = "email", column = "email"),@Result(property = "age", column = "age"),@Result(property = "createdTime", column = "created_time")})User selectUserByIdWithAnnotation(@Param("id") Integer id);
}