MyBatis基础操作完整指南

文章目录

MyBatis简介
环境搭建
- Maven依赖
- 数据库表结构
核心配置
基础CRUD操作
- Mapper接口
- [Mapper XML映射文件](#Mapper XML映射文件)
- 工具类
- 测试类
动态SQL
- 常用标签
高级特性

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：

xml 复制代码

<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：

sql 复制代码

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 复制代码

<?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>
    <!-- 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：

properties 复制代码

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：

java 复制代码

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;
    }
    
    @Override
    public 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：

java 复制代码

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 复制代码

<?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.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 SET
            username = #{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_time
        FROM user
        WHERE id = #{id}
    </select>
    
    <!-- 查询所有用户 -->
    <select id="selectAllUsers" resultMap="userResultMap">
        SELECT id, username, email, age, created_time
        FROM user
        ORDER 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_time
        FROM user
        WHERE username LIKE CONCAT('%', #{username}, '%')
    </select>
    
</mapper>

工具类

创建MyBatis工具类：

java 复制代码

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SqlSessionFactory
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    // 获取SqlSession
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
    
    // 获取自动提交的SqlSession
    public static SqlSession getSqlSession(boolean autoCommit) {
        return sqlSessionFactory.openSession(autoCommit);
    }
}

测试类

创建测试类验证CRUD操作：

java 复制代码

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", "zhangsan@example.com", 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("updated@example.com");
                
                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

xml 复制代码

<!-- if标签：条件判断 -->
<select id="selectUsersByCondition" parameterType="User" resultMap="userResultMap">
    SELECT * FROM user
    WHERE 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 user
    WHERE id IN
    <foreach collection="list" item="id" open="(" separator="," close=")">
        #{id}
    </foreach>
</select>

高级特性

一对一关联映射

xml 复制代码

<!-- 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.amount
    FROM user u
    LEFT JOIN order o ON u.id = o.user_id
    WHERE u.id = #{id}
</select>

一对多关联映射

xml 复制代码

<!-- 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.amount
    FROM user u
    LEFT JOIN order o ON u.id = o.user_id
    WHERE u.id = #{id}
</select>

分页查询

xml 复制代码

<!-- 分页查询 -->
<select id="selectUsersWithPage" parameterType="map" resultMap="userResultMap">
    SELECT * FROM user
    ORDER BY created_time DESC
    LIMIT #{offset}, #{pageSize}
</select>

<!-- 查询总数 -->
<select id="countUsers" resultType="int">
    SELECT COUNT(*) FROM user
</select>

使用注解方式

java 复制代码

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);
}