MyBatis(1) 实现增删改查

简介

2.第一个Mybatis程序

搭建数据库

create database `mybatis`;
use `mybatis`;

create table `user`(
	`id` INT(20) NOT NULL PRIMARY KEY,
	`name` VARCHAR(30) DEFAULT NULL,
	`pwd` VARCHAR(30) DEFAULT NULL)
	ENGINE =INNODB DEFAULT CHARSET=UTF8;
)
	insert into `user`(`id`,`name`,`pwd`) values
	(1,'狂神','123455'),
	(2,'张三','123423'),
	(3,'李四','23423234'),

新建项目

1.新建一个普通的maven项目

2 删除src目录

3 导入maven依赖

<!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.11</version>
        </dependency>

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.4</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>

2,2 创建一个模块

• 创建mybatis的核心配置文件

<?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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC">
                <property name="..." value="..."/>
            </transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8" />
                <property name="username" value="root"/>
                <property name="password" value="love819099119"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

• 编写mybatis工具类

//sqlSessionFactory --> sqlSession
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try{
            //使用Mybatis第一步：获取sqlSessionFactory对象
            String resource ="mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        }catch (IOException e){
            e.printStackTrace();
        }
    }
    //既然有了SqlSessionFactory，顾名思义，我们就可以从中获得SqlSession的实例了
    //SqlSession完全包含了面向数据库执行SQL命令所需的所有方法。
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

2.3 编写代码

实体类

package com.hao.pojo;

import lombok.Data;

@Data
public class User {
    private int id;
    private String name;
    private String pwd;

}

Dao接口

import java.util.List;

public interface UserDao {
    List<User> getUserList();
}

接口实现类由原来的UserDaoImpl转变为一个Mapper配置文件

<mapper namespace="com.hao.dao.UserDao">
<!--    select查询语句-->
    <select id="getUserList" resultType="com.hao.pojo.User">
        select * from mybatis.user
    </select>

</mapper>

2.4 、测试

你们可能遇到的问题

绑定接口错误

方法名不对

返回类型不对

maven导出资源

3 CRUD

1 、namespace

namespace中的包名要和 Dao/mapper 接口的包名一致

2、select

选择，查询语句

• id：就是对应的namespace中的方法名；
• resultType：Sql语句执行的返回值！
• parameterType :参数类型！

1 编写接口

//根据ID查询用户
User getUserById(int id);

2 编写对应的mapper中的sql语句

  <select id="getUserById" parameterType="int" resultType="com.hao.pojo.User">
        select * from mybatis.user where id =#{id}
    </select>

3测试

 @Test
    public void getUserById(){
        SqlSession sqlSession =MybatisUtils.getSqlSession();

        UserDao mapper =sqlSession.getMapper(UserDao.class);

        User user =mapper.getUserById(1);

        System.out.println(user);

        sqlSession.close();
    }

3 Insert

<insert id="addUser" parameterType="com.hao.pojo.User">
        insert into mybatis.user (id,name,pwd) values(#{id},#{name},#{pwd});

    </insert>

4 Update

<update id="updateUser" parameterType="com.hao.pojo.User">
        update mybatis.user set name=#{name},pwd=#{pwd} where id =#{id};
    </update>

5 Delete

 <delete id="deleteUser" parameterType="int">
        delete from mybatis.user where id=#{id};
    </delete>

注意点

• 增删改需要提交事务