Mybatis学习笔记(1)

Mybatis自学(1)

1、什么是MyBatis

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SQL语句中的insert语句返回值是插入的数据的条数，若插入失败，则返回值为0。

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实体类：属性私有、方法公有。

补充

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2、第一个Mybatis程序

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搭建环境

  • 搭建数据库
create DATABASE mybatis;

use mybatis;

create table user(
	id int(20) not null,
	name varchar(30) DEFAULT null,
	pwd VARCHAR(30) DEFAULT null,
	PRIMARY KEY(id)
)ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT 
INTO USER 
VALUES
(1,'蔡伟','123456'),
(2,'昊炜','142536'),
(3,'磊子','512364')
  • 新建项目

a)新建一个普通的maven项目

b)删除src目录

c)导入maven依赖



    
    
        mysql
        mysql-connector-java
        8.0.26
    
    
    
        org.mybatis
        mybatis
        3.5.7
    
    
    
        junit
        junit
        4.13.2

d）创建一个模块

  • 编写mybatis的核心配置文件

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
  • 编写 mybatis的工具类

MybatisUtils.java

package top.gujiakai.utils;

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;

/**
 * Author: Gu Jiakai
 * Date: 2021/10/15 10:18
 * FileName: MybatisUtils
 * Description:
 */
//SqlSessionFactory -->sqlsession
public class MybatisUtils {
    //提升作用域
    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 (Exception e) {
            e.printStackTrace();
        }
    }

//    既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。
//    SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。
    public static SqlSession getSqlSession(){
//        SqlSession sqlSession = sqlSessionFactory.openSession();
//        return sqlSession;
        return sqlSessionFactory.openSession();
    }
}

e）编写代码

  • 实体类
package top.gujiakai.pojo;

/**
 * Author: Gu Jiakai
 * Date: 2021/10/15 11:04
 * FileName: User
 * Description:
 */
//实体类
public class User {
    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
}
  • Dao接口

UserDao.java

package top.gujiakai.dao;

import top.gujiakai.pojo.User;

import java.util.List;

/**
 * Author: Gu Jiakai
 * Date: 2021/10/15 11:07
 * FileName: UserDao
 * Description:
 */
public interface UserDao {
    List getUserList();
}
  • 接口实现类

接口实现类由原来的UserDaolmpl转变为一个Mapper配置文件。

UserMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>

f)测试

  • junit测试
报错集合：
a)org.apache.ibatis.binding.BindingException: Type interface top.gujiakai.dao.UserDao is not known to the MapperRegistry.
没有在mybatis-config.xml中配置mapper。
核心配置文件中注册mappers。
b)Could not find resource top/gujiakai/dao/UserMapper.xml
资源过滤问题

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  • junit测试

UserDaoTest.java

package top.gujiakai.dao;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import top.gujiakai.pojo.User;
import top.gujiakai.utils.MybatisUtils;

import java.util.List;

/**
 * Author: Gu Jiakai
 * Date: 2021/10/15 11:21
 * FileName: UserDaoTest
 * Description:
 */
public class UserDaoTest {
    @Test
    public void test(){
//        第1步：获取sqlsession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
//         方式一：getMapper
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List userList = userDao.getUserList();

        for(User user:userList){
            System.out.println(user);
        }

        //关闭sqlSession
        sqlSession.close();
    }
}

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3、增删改查实现

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  • 增删改需要提交事务。

UserMapper.java

package top.gujiakai.dao;

import top.gujiakai.pojo.User;

import java.util.List;

/**
 * Author: Gu Jiakai
 * Date: 2021/10/15 11:07
 * FileName: UserDao
 * Description:
 */
public interface UserMapper {
//    查询全部用户。
    List getUserList();
//    根据ID查询用户。
    User getUserByID(int id);
    //insert一个用户。
    int addUser(User user);

//    修改用户。
    int updateUser(User user);
    //删除一个用户。
    int deleteUser(int id);
}

UserMapper.xml

<?xml version="1.0" encoding="GBK" ?>




    
    
    


    
        insert into mybatis.user(id,name,pwd) values(#{id},#{name},#{pwd})
    
    
    
        update mybatis.user
        set name=#{name},pwd=#{pwd}
        where id=#{id};
    

    
        delete from mybatis.user where id=#{id}

UserDaoTest.java

package top.gujiakai.dao;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import top.gujiakai.pojo.User;
import top.gujiakai.utils.MybatisUtils;

import java.util.List;

/**
 * Author: Gu Jiakai
 * Date: 2021/10/15 11:21
 * FileName: UserDaoTest
 * Description:
 */
public class UserDaoTest {
    @Test
    public void test() {
//        第1步：获取sqlsession对象
        SqlSession sqlSession = null;

        try {
            sqlSession = MybatisUtils.getSqlSession();
            //         方式一：getMapper
            //        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
            //        List userList = userDao.getUserList();


            //        方式二：
            List userList = sqlSession.selectList("top.gujiakai.dao.UserMapper.getUserList");

            for (User user : userList) {
                System.out.println(user);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            //关闭sqlSession
            sqlSession.close();
        }
    }

    @Test
    public void getUserByID(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserByID(1);
        System.out.println(user);
        sqlSession.close();
    }

    //增删改需要提交事务。
    @Test
    public void addUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        int res = mapper.addUser(new User(4, "阿豪", "12542"));
        if(res>0){
            System.out.println("插入成功！");
        }
        //提交事务。
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void updateUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        mapper.updateUser(new User(4,"小辫子","123456"));

        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void deleteUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.deleteUser(3);
        sqlSession.commit();
        sqlSession.close();
    }
}

4、错误排查指导

读错从后往前读。

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5、Map和模糊查询拓展

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UserMapper.java

package top.gujiakai.dao;

import top.gujiakai.pojo.User;

import java.util.List;
import java.util.Map;

/**
 * Author: Gu Jiakai
 * Date: 2021/10/15 11:07
 * FileName: UserDao
 * Description:
 */
public interface UserMapper {

    List getUserLike(String value);

//    查询全部用户。
    List getUserList();
//    根据ID查询用户。
    User getUserByID(int id);

    User getUserByID2(Map map);
    //insert一个用户。
    int addUser(User user);

    int addUser2(Map map);

//    修改用户。
    int updateUser(User user);
    //删除一个用户。
    int deleteUser(int id);
}

UserMapper.xml

<?xml version="1.0" encoding="GBK" ?>




    


    
    
    

    


    
        insert into mybatis.user(id,name,pwd) values(#{id},#{name},#{pwd})
    





    
    
        update mybatis.user
        set name=#{name},pwd=#{pwd}
        where id=#{id};
    

    
        delete from mybatis.user where id=#{id}

UserDaoTest.java

package top.gujiakai.dao;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import top.gujiakai.pojo.User;
import top.gujiakai.utils.MybatisUtils;

import java.util.HashMap;
import java.util.List;

/**
 * Author: Gu Jiakai
 * Date: 2021/10/15 11:21
 * FileName: UserDaoTest
 * Description:
 */
public class UserDaoTest {

    @Test
    public void getUserLike(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        List userList = mapper.getUserLike("%蔡%");

        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }

    @Test
    public void test() {
//        第1步：获取sqlsession对象
        SqlSession sqlSession = null;

        try {
            sqlSession = MybatisUtils.getSqlSession();
            //         方式一：getMapper
            //        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
            //        List userList = userDao.getUserList();


            //        方式二：
            List userList = sqlSession.selectList("top.gujiakai.dao.UserMapper.getUserList");

            for (User user : userList) {
                System.out.println(user);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            //关闭sqlSession
            sqlSession.close();
        }
    }

    @Test
    public void getUserByID(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserByID(1);
        System.out.println(user);
        sqlSession.close();
    }

    @Test
    public void getUserByID2(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        HashMap map = new HashMap();

        map.put("helloID",1);
        mapper.addUser2(map);
        sqlSession.close();
    }

    //增删改需要提交事务。
    @Test
    public void addUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        int res = mapper.addUser(new User(4, "阿豪", "12542"));
        if(res>0){
            System.out.println("插入成功！");
        }
        //提交事务。
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void addUser2(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        HashMap map = new HashMap<>();
        map.put("userID",5);
        map.put("userName","caiwei2333");
        map.put("passWord","123456");

        mapper.addUser2(map);

        sqlSession.close();
    }


    @Test
    public void updateUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        mapper.updateUser(new User(4,"小辫子","123456"));

        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void deleteUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.deleteUser(3);
        sqlSession.commit();
        sqlSession.close();
    }
}
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