Mybatis中的CRUD

CRUD

增加(Create)、检索(Retrieve)、更新(Update)和删除(Delete)

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
• resultType：sql语句执行的返回值
• parameterType：参数类型

<?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">

        <!--命名空间=绑定的一个对应的Dao/Mapper接口-->
<mapper namespace="com.linfeng.dao.UserMapper">

<select id="getUserList" resultType="com.linfeng.pojo.user">
select * from mybatis.user;
  </select>
<!-- #{}取变量-->
    <select id="getUserByid" parameterType="int" resultType="com.linfeng.pojo.user">
        select *from mybatis.user where id = #{id}
    </select>

    <insert id="addUser" parameterType="com.linfeng.pojo.user">
        insert into mybatis.user (id, name, pwd) value(#{id},#{name},#{pwd});
    </insert>

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


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

在这里插入代码片package com.linfeng.dao;


import com.linfeng.pojo.user;
import com.linfeng.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {
    @Test
    public void test(){
        //获得sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //执行
        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 = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        user user = mapper.getUserByid(1);
        System.out.println(user);

        sqlSession.close();
    }

    @Test
    //增删改需要提交事务
    public void addUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int i = mapper.addUser(new user(4, "baby", "123444"));
        if (i > 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,"hhh","123444"));
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void deleteUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.deleteUser(4);
        sqlSession.commit();
        sqlSession.close();
    }
}

package com.linfeng.dao;
import com.linfeng.pojo.user;
import java.util.List;

public interface UserMapper {
    //查询全部用户
    List<user> getUserList();
    //根据id查询用户
    user getUserByid(int i);
    //insert用户
    int addUser(user user);
    //修改用户
    int updateUser (user user);
    //删除用户
    int deleteUser(int id);
}

万能map

假设，我们的实例类，或者数据库中的表，字段或者参数过多，我们应该考虑使用map!

接口

int addUser2(Map map);

mapper

    insert into `user`(id, name, pwd) values (#{userId},#{userName},#{password})

Map传递参数，直接在sql中取出key即可！

对象传递参数，直接在sql中取对象的属性即可！

只有一个基本类型的情况下，可以直接在sql中取到！

多个参数用Map，或者注解！

 public void addUser2(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        Map<String, Object> map = new HashMap<String, Object>();

        map.put("userid",5);
        map.put("userName","hello");
        map.put("password","123333");
        
        mapper.addUser2(map);//传一个map
        
        sqlSession.close();
    }

思考题

模糊查询怎么写？

java代码执行的时候，传递通配符%

  List<User> userList = userMapper.getUserLike("%z%");

在sql中拼接使用通配符 （不推荐，容易引起sql注入问题）

 <!--  select id, name, pwd from `user` where id = ?   -->
    <!--  select id, name, pwd from `user` where id = 1      一般情况-->
    <!--  select id, name, pwd from `user` where id = 1 or 1=1   sql注入情况-->
    <select id="getUserLike" resultType="com.zyy.pojo.User" parameterType="string">
        select id, name, pwd from `user` where name like "%"#{value}"%"
    </select>