【MyBatis】MyBatis简介+MyBatis的快速入门（Mapper代理开发）-526互联

MyBatis简介

JDBC的缺点

硬编码
注册驱动，获取连接
SQL语句
操作繁琐
手动设置参数
手动封装结果集

MyBatis的快速入门——Mapper代理开发

MyBatis核心配置文件——替换JDBC的连接信息，解决硬编码问题

mybatis-config.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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--数据库连接信息-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="000905"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!--加载sql映射文件-->
        <mapper resource="com/EveX/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

编写SQL映射文件——统一管理sql语句，解决硬编码问题
命名规范：映射表对应的类Xxx，映射文件命名为XxxMapper

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.EveX.mapper.UserMapper">
    <select id="selectAll" resultType="com.EveX.domain.User">
        select * from tb_user;
    </select>
</mapper>

定义与SQL映射文件同名的Mapper接口，并且将Mapper接口和SQL映射文件放在同一目录下

这样放置文件，编译生成的字节码文件是在同一个目录下
设置SQL映射文件的namespace属性为Mapper接口的全限定名
在Mapper接口中定义方法，方法名是SQL映射文件中sql语句的id，需要保持参数类型和返回值类型与sql语句一致

UserMapper.java

package com.EveX.mapper;

import com.EveX.domain.User;

import java.util.List;

public interface UserMapper {
    List<User> selectAll();
}

通过SqlSession的getMapper方法获取Mapper接口的代理对象，然后调用对应方法执行相应sql语句

mybatisQuickDemo.java

package com.EveX;

import com.EveX.domain.User;
import com.EveX.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 java.io.InputStream;
import java.io.IOException;
import java.util.List;

/**
 * Mybatis快速入门——Mapper代理开发代码
 */
public class mybatisQuickDemo {
    public static void main(String[] args) throws IOException {
        /*加载mybatis的核心配置文件，获取SqlSessionFactory*/
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        /*获取SqlSession，用来执行sql*/
        SqlSession sqlSession = sqlSessionFactory.openSession();

        /*执行sql*/
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = userMapper.selectAll();

        System.out.println(users);

        /*释放资源*/
        sqlSession.close();
    }
}

注意：pom.xml中mysql驱动依赖版本需要和连接的数据库版本相对应。具体可以参照IDEA连接数据库下载的驱动版本，如下

MyBatis核心配置文件细节

(1) Mapper接口名称和SQL映射文件名称相同，且在同一目录下，可以使用包扫描的方式简化SQL映射文件的加载
(2)类型别名设置：默认情况下的别名：不需要再使用类的全限定名，类名也不再区分大小写，这样SQL映射文件中的resultType就可以简化书写。也可以自定义别名

mybatis-config.xml包扫描加载SQL映射文件

    <mappers>
        <!--加载sql映射文件-->
<!--        <mapper resource="com/EveX/mapper/UserMapper.xml"/>-->
        <!--Mapper接口名称和SQL映射文件名称相同，且在同一目录下，
        可以使用包扫描的方式简化SQL映射文件的加载-->
        <package name="com/EveX/mapper"/>
    </mappers>

mybatis-config.xml类型别名设置

    <!--类型别名设置-->
    <typeAliases>
        <!--相当于给被扫描的包下的类起了别名，
        默认情况下的别名：不需要再使用类的全限定名，类名也不再区分大小写
        这样SQL映射文件中的resultType就可以简化书写
        -->
        <package name="com.EveX.domain"/>
    </typeAliases>

配置文件完成SQL增删改查

SQL映射文件细节

实体类属性名和数据库表列名不一致如何解决？

参数占位符

SQL语句设置多个参数的方式

映射接口：BrandMapper.java

    /*散装参数，用注解Param与SQL参数占位符映射*/
    List<Brand> selectByCondition(@Param("status") int status,
                                  @Param("companyName") String companyName,
                                  @Param("brandName") String brandName);

    /*实体类封装参数*/
    List<Brand> selectByCondition(Brand brand);

    /*map集合封装参数*/
    List<Brand> selectByCondition(Map map);

SQL配置文件BrandMapper.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.EveX.mapper.BrandMapper">

    <!--用结果映射解决类属性和数据库字段名称不一致的问题-->

    <resultMap id="brandMap" type="Brand">
        <result column="brand_name" property="brandName"></result>
        <result column="company_name" property="companyName"></result>
    </resultMap>

    <select id="selectAll" resultMap="brandMap">
        select * from tb_brand;
    </select>


    <!--<select id="selectAll" resultType="com.EveX.domain.Brand">
        select * from tb_brand;
    </select>-->

    <select id="selectById" resultMap="brandMap">
        select * from tb_brand where id = #{id};
    </select>

    <select id="selectByCondition" resultMap="brandMap">
        select *
        from tb_brand
        where status = #{status}
          and company_name like #{companyName}
          and brand_name like #{brandName};
    </select>


</mapper>

测试代码

        /*散装参数*/
        List<Brand> brands = brandMapper.selectByCondition(status, companyName, brandName);
        System.out.println(brands);

        /*实体类封装参数*/
        Brand brand = new Brand();
        brand.setStatus(status);
        brand.setCompanyName(companyName);
        brand.setBrandName(brandName);
        List<Brand> brands1 = brandMapper.selectByCondition(brand);
        System.out.println(brands1);

        /*map集合封装参数*/
        Map map = new HashMap<>();
        map.put("status", status);
        map.put("companyName", companyName);
        map.put("brandName", brandName);
        List<Brand> brands2 = brandMapper.selectByCondition(map);
        System.out.println(brands2);

动态SQL

多条件-动态查询

SQL配置文件BrandMapper.xml

    <select id="selectByCondition" resultMap="brandMap">
        select *
        from tb_brand
        <where>
            <if test="status != null">
                and status = #{status}
            </if>
            <if test="companyName != null and companyName != ''">
                and company_name like #{companyName}
            </if>
            <if test="brandName != null and brandName != ''">
                and brand_name like #{brandName};
            </if>
        </where>
    </select>

单条件-动态查询

其中<choose>相当于switch，<when>相当于case，<otherwise>相当于default

SQL配置文件BrandMapper.xml

    <select id="selectByConditionSingle" resultMap="brandMap">
        select *
        from tb_brand
        <where>
            <choose>
                <when test="status != null">
                    status = #{status}
                </when>
                <when test="companyName != null and companyName != ''">
                    company_name like #{companyName}
                </when>
                <when test="brandName != null and brandName != ''">
                    brand_name like #{brandName};
                </when>
                <otherwise>

                </otherwise>
            </choose>
        </where>
    </select>

MyBatis事务

SQL配置文件BrandMapper.xml

    <insert id="add" useGeneratedKeys="true" keyProperty="id">
        insert into tb_brand (brand_name, company_name, ordered, description, status)
        VALUES (#{brandName}, #{companyName}, #{ordered}, #{description}, #{status});
    </insert>

MyBatis参数传递

数组参数

mybatis会将数组参数封装为一个Map集合，默认情况下：数组名为array，可以使用@Param注解改变map集合的默认key的名称

遍历数组用<foreach>

SQL配置文件BrandMapper.xml

    <delete id="deleteByIds">
        delete
        from tb_brand
        where id in
        <foreach collection="ids" item="id" separator="," open="(" close=")">
            #{id}
        </foreach>
        ;
    </delete>

注解完成SQL增删改查

mybatis-plus springboot mybatis mapper

mybatis方法mapper

mybatis方式mapper

mybatis mapper and tk

mapper-locations mapperlocations mybatis-plus

libraries mybatis mapper common

mybatis类型mapper clob

mybatis-plus mybatis mapper plus

association collection mybatis mapper