MyBatis

官网：https://mybatis.org/mybatis-3/zh/index.html

快速入门

创建user表，添加数据
创建模块，导入坐标

编写Mybatis核心配置文件-->替换链接信息，解决硬编码问题

<?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">
<!--                数据库的链接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
<!--        加载sql的映射文件-->
        <mapper resource="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

<?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">
<!--namespace名称空间-->
<mapper namespace="test">
    <select id="selectAll" resultType="com.itheima.pojo.User">
        select * from tb_user;
    </select>
</mapper>

编码
1. 定义POJO类
2. 加载核心文件，获取SqlSessionFactory
3. 获取SqlSession对象，执行SQL语句

释放资源

package com.itheima;
 
import com.itheima.pojo.User;
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;
import java.util.List;
 
/**
 * mybatis快速入门
 */
public class MybatisDemo {
    public static void main(String[] args) throws IOException {
        //1.加载mybatis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);
 
        //2.获取sqlSession对象，用它执行sql
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //3.执行sql
        List<User> users = sqlSession.selectList("test.selectAll");
 
        System.out.println(users);
        sqlSession.close();
    }
}

解决sql映射文件警告信息

Mapper代理开发

目的：解决原生方式中硬编码

简化后期执行SQL

1 2	`//3.执行sql` `List<User> users = sqlSession.selectList("test.selectAll");`

//3.获取接口代理对象
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
//4.执行方法，执行sql
userMapper.selectAll();

步骤：

定义SQL映射文件同名的Mapper接口，并且将Mapper接口和SQL映射文件放置在同一目录下（将SQL映射文件放在resource下与Mapper接口相同的包中，compiler后生成的classes中即在同一目录）

设置SQL映射文件的namespace属性为Mapper接口全限定名

<!--namespace名称空间-->
<mapper namespace="com.itheima.mapper.UserMapper">
    <select id="selectAll" resultType="com.itheima.pojo.User">
        select * from tb_user;
    </select>
</mapper>

在Mapper接口中定义方法，方法名就是SQL映射文件中sql语句的id，并保持参数类型和返回值类型一致

** 不要忘记改config中映射文件的路径 **
编码
1. 通过SqlSession的getMapper方法获取Mapper接口的代理对象
2. 调用对应方法完成sql的执行
  
  ?
  1
  2
  3
  4
  //3.获取接口代理对象
  UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
  //4.执行方法，执行sql
  List<User> users = userMapper.selectAll();

　　细节：如果Mapper接口名称和SQL映射文件名称相同，并在同一目录下，则可以使用包扫描的方式简化SQL映射文件的而加载

    <mappers>
<!--        加载sql的映射文件-->
<!--        <mapper resource="com/itheima/mapper/UserMapper.xml"/>-->
<!--   　　  Mapper代理方式-->
        <package name="com.itheima.mapper"/>
    </mappers>

MyBatis核心配置文件详解

<mapper namespace="com.itheima.mapper.BrandMapper">
<!-- SQL片段 -->
    <sql id="brand_column">
        id,brand_name brandName,company_name companyName,ordered,description,status
    </sql>
    <select id="selectAll" resultType="Brand">
        select <include refid="brand_column"/>
        from tb_brand;
    </select>
</mapper>

<!-- 
    resultMap：
        1.定义resultMap标签
        2.<select>标签中使用resultMap属性替换resultType属性   
    id：唯一标识
    type：映射的类型，支持别名
    
    -->
    <resultMap id="brandResultMap" type="Brand">
<!--        
        id：完成主键字段映射
            column：表的列名
            property：实体类的属性名
        result：完成一般字段的映射
            column：表的列名
            property：实体类的属性名
-->
        <result column="brand_name" property="brandName"></result>
        <result column="company_name" property="companyName"></result>
    </resultMap>
    <select id="selectAll" resultMap="brandResultMap">
        select *
        from tb_brand;
    </select>
</mapper>

配置文件完成增删改查

    <resultMap id="brandResultMap" type="Brand">
        <result column="brand_name" property="brandName"></result>
        <result column="company_name" property="companyName"></result>
    </resultMap>
    <select id="selectAll" resultMap="brandResultMap">
        select *
        from tb_brand;
    </select>
    <select id="selectById" parameterType="int" resultMap="brandResultMap">
--         select * from ${tb_brand} where id = #{id};
--         select * from tb_brand where id 小于号 #{id};
--         select * from tb_brand where id &lt; #{id};
        select *
        from tb_brand
        where id
               <![CDATA[
                    <=
                ]]>
              #{id}
    </select>