Mybatis实现增删改查-mybatis的核心

电玩女神 2023-07-15 09:17 25阅读 0赞

**CRUD（增删改查）–mybatis的核心**  
搭建好mybatis环境以后可以实现对数据库的增删改查等操作  
**结构目录**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mzg5NDc3MQ_size_16_color_FFFFFF_t_70]  
**1.namespace**  
namespace中的包名要和Dao/mapper接口中的包名一致！

**2.过程**

*  id：就是对应的namespace中的方法名
 *  parameterType：参数类型
 *  resultType：sql语句执行的返回值

**1.编写接口**

package com.superman.dao;
    
    import com.superman.pojo.User;
    
    import java.util.List;
    
    public interface UserMapper { 
        //查询全部用户
        List<User> getUserList();
    
        //根据用户id查询
        User getUserById(int id);
    
        //增加一个用户
        int addUser(User user);
    
        //修改一个用户
        int updateUser(User user);
    
        //删除一个用户
        int deleteUser(int id);
    }

**2.填写对应的mapper中的sql语句**

<?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.superman.dao.UserMapper">
    
        
        <select id="getUserList" resultType="com.superman.pojo.User">
            select * from mybatis.user;
        </select>
    
    
        <select id="getUserById" resultType="com.superman.pojo.User" parameterType="int">
            select * from mybatis.user where id=#{ id};
        </select>
    
    
        
        <insert id="addUser" parameterType="com.superman.pojo.User">
            insert into mybatis.user(id,username,birthday,sex,address) values (#{ id},#{ username},#{ birthday},#{ sex},#{ address});
        </insert>
    
    
        <update id="updateUser" parameterType="com.superman.pojo.User">
            update mybatis.user set username=#{ username},address=#{ address},birthday=#{ birthday} where id=#{ id};
        </update>
    
    
        <delete id="deleteUser" parameterType="int">
            delete from mybatis.user where id=#{ id};
        </delete>
    </mapper>

3.测试

package com.superman.dao;
    
    import com.superman.pojo.User;
    import com.superman.utils.MybatisUtil;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    import java.util.List;
    
    public class UserDaoTest { 
    
        @Test
        public void test() { 
            //第一步：获得sqlsession对象
            SqlSession sqlSession = MybatisUtil.getSqlSession();
            //方式一：执行SQL
            UserMapper mapper=sqlSession.getMapper(UserMapper.class);
            List<User> userList=mapper.getUserList();
    
            for (User user : userList) { 
                System.out.println(user);
            }
    
        //关闭SqlSession
            sqlSession.close();
        }
    
        @Test
        public void getUserById(){ 
            SqlSession sqlSession=MybatisUtil.getSqlSession();
            UserMapper mapper=sqlSession.getMapper(UserMapper.class);
            User user=mapper.getUserById(1);
            System.out.println(user);
            sqlSession.close();
        }
    
        @Test
        public  void addUser(){ 
            SqlSession sqlSession=MybatisUtil.getSqlSession();
            UserMapper mapper=sqlSession.getMapper(UserMapper.class);
            mapper.addUser(new User(5,"caiji","20201005","男","北京"));
            List<User> userList=mapper.getUserList();
            for (User user : userList) { 
                System.out.println(user);
            }
    
            //提交事务，负责数据库将不会发生变化，即使输出打印时显示插入成功
            sqlSession.commit();
            sqlSession.close();
        }
    
        @Test
        public void updateUser(){ 
            SqlSession sqlSession=MybatisUtil.getSqlSession();
            UserMapper mapper=sqlSession.getMapper(UserMapper.class);
            mapper.updateUser(new User(5,"zhaoxuan","20201515","女","太谷"));
            sqlSession.commit();
            sqlSession.close();
        }
    
        @Test
        public void deleteUser(){ 
            SqlSession sqlSession=MybatisUtil.getSqlSession();
            UserMapper mapper=sqlSession.getMapper(UserMapper.class);
            mapper.deleteUser(5);
            sqlSession.commit();
            sqlSession.close();
        }
    
    }

**注意点：  
执行sql语句时，增删改必须要提交事务，sqlSession.commit();，否则无法对数据库产生语句效果  
代码中没有使用mybatis中建议的代码格式，但是每次都需要在最后加上sqlSession.close();**

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