MyBatis学习随笔

第一个MyBatis项目

创建项目
导入maven依赖,根据需要选择性添加mysql/oracle,spring,spring-mybatis等依赖,这里就不一一列出了

<dependency>

            <groupId>org.mybatis</groupId>

            <artifactId>mybatis</artifactId>

            <version>3.4.1</version>

        </dependency>

创建mybatis配置文件

<?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>

    <!--加载外部配置文件-->

    <properties resource="mysql8.properties"></properties>

    <environments default="development">

        <environment id="development">

            <transactionManager type="JDBC"/>

            <dataSource type="POOLED">

                <!--

                    这里的value可以使用常量

                    同时可以使用${}在配置文件中读取

                    后期整合spring就不需在此配置

                -->

                <property name="driver" value="${driverClassName}"/>

                <property name="url" value="${url}"/>

                <property name="username" value="${username}"/>

                <property name="password" value="${password}"/>

            </dataSource>

        </environment>

    </environments>

    <mappers>

        <!--这里拷贝加载的mapper文件的全路径-->

        <mapper resource="com/offcn/mapper/CustomerMapper.xml"/>

    </mappers>

</configuration>

MyBatis基本配置文件

创建mapper的配置文件

<?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.offcn.mapper.CustomerMapper">

    <!--根据cust_id查询客户-->

    <select id="selectCustomerById" parameterType="Int" resultType="com.offcn.bean.Customer">

      SELECT * FROM `customer` WHERE cust_id  = #{cust_id}

    </select>

</mapper>

Mapper.xml

创建mapper.xml对应的接口,该接口名要和mapper文件名完全一致

package com.offcn.mapper;

import com.offcn.bean.Customer;

import org.springframework.stereotype.Repository;

@Repository

public interface CustomerMapper {

    public Customer selectCustomerById(Integer id);

}

Bean对象代码

package com.offcn.bean;

import lombok.Getter;

import lombok.Setter;

import lombok.ToString;

import org.springframework.stereotype.Component;

/**

 * @author 张瑞丰

 * @description 客户表bean

 * @date 2019/4/19

 */

@Getter@Setter@ToString@Component

public class Customer {

    private Integer custId;

    private String custName;

    private String custProfession;

    private String custPhone;

    private String email;

}

测试类代码

    @Test

    public void test() throws IOException {

        //创建SqlSessionFactoryBuilder

        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();

        //读取配置文件

        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis.xml");

        //获取session工厂

        SqlSessionFactory sessionFactory = sqlSessionFactoryBuilder.build(resourceAsStream);

        //获取会话

        SqlSession sqlSession = sessionFactory.openSession();

        //执行sql,并得到返回值

        Customer result = (Customer)sqlSession.selectOne("selectCustomerById", 2);

        //获取结果

        System.out.println(result);

    }

输出结果:Customer(custId=null, custName=null, custProfession=null, custPhone=null, email=libai@163.com)

只有email正常输出,其余字段都未正常输出,原因:表中字段除email外,名为cust_xx而bean则为custXx,因列名和字段名不一致导致,解决方案如下:

　　在mapper中创建resultMap将表中字段和bean的属性进行映射,同时要修改select的ResultMap为其id,一定不能打错,打错会报一万个错误
　　在mybatis全局配置文件中开启驼峰转下划线
在select语句中给列名起别名的形式

<?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.offcn.mapper.CustomerMapper">

    <!--映射表字段和列名 type为bean的全类名-->

    <resultMap id="BaseResultMap" type="com.offcn.bean.Customer">

        <id column="cust_id" property="custId"></id>

        <result column="cust_name" property="custName"></result>

        <result column="cust_profession" property="custProfession"></result>

        <result column="cust_phone" property="custPhone"></result>

        <result column="email" property="email"></result>

    </resultMap>

    <!--根据cust_id查询客户-->

    <select id="selectCustomerById" parameterType="Int" resultMap="BaseResultMap">

      SELECT * FROM `customer` WHERE cust_id  = #{cust_id}

    </select>

</mapper>

巴特西

MyBatis笔记(一)

MyBatis学习随笔

第一个MyBatis项目

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