CRUD增删改查

增删改查实现

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

package com.god.dao;

import com.god.pojo.User;

import java.util.List;

public interface UserMapper {
    // 查询所有用户
    List<User> 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);

    //删除用户
    int deleteUser(int id);
}

2、编写对应的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">
<!--namespace= 绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.god.dao.UserMapper">
    <!--select 查询语句-->
    <select id="getUserList" resultType="com.god.pojo.User">
        select * from mybatis.user;
    </select>
    <select id="getUserById" parameterType="int" resultType="com.god.pojo.User">
        select * from mybatis.user where id = #{id};
    </select>

    <!--对象中的属性，可以直接取出来-->
    <insert id="addUser" parameterType="com.god.pojo.User">
        insert into mybatis.user (id,name,pwd) values (#{id},#{name},#{pwd});
    </insert>

    <update id="updateUser" parameterType="com.god.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>

3、测试 增删改需要提酒事务

package com.god.dao;

import com.god.pojo.User;
import com.god.utils.MybatisUtils;
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 = MybatisUtils.getSqlSession();
        try {
            //方式一：getMapper
            UserMapper userDao = sqlSession.getMapper(UserMapper.class);
            List<User> userList =userDao.getUserList();

            //方式二
            //List<User> userList = sqlSession.selectList("com.god.dao.UserDao.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();
    }

    //增删改查需要提交事务
    @Test
    public void addUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int res =mapper.addUser(new User(4,"欧布","147"));
        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,"赛迦","520"));
        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();

    }
}

3、Insert

4、update

5、Delete

注意点：增删改需要提交事务！

6、分析错误：

• 标签不要匹配错
• resource绑定mapper，需要使用路径
• 程序配置文件必须符合规范<mybatis-config.xml>
• NullPointerException，没有注册到资源
• 输出的xml文件中存在中文乱码问题
• maven资源没有导出问题

7、万能Map

假设，我们的实体类，或者数据库中的表，字段或参数过多，我们应当考虑使用map
UserMapper.java

    //insert一个用户
    int addUser (User user);
       //万能Map
    int addUser2 (Map<String,Object> map);

UserMapper.xml

   <!--对象中的属性，可以直接取出来-->
    <insert id="addUser" parameterType="com.god.pojo.User">
        insert into mybatis.user (id,name,pwd) values (#{id},#{name},#{pwd});
    </insert>
    <!--传递map的key-->
    <insert id="addUser2" parameterType="map">
        insert into mybatis.user (id,name,pwd) values (#{userid},#{username},#{passWord});
    </insert>

UserMapperTest.java

    //增删改查需要提交事务
    @Test
    public void addUser() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int res =mapper.addUser(new User(4,"欧布","147"));
        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);
        Map<String,Object>map=new HashMap<String,Object>();
        map.put("userid",4);
        map.put("username","HELLO");
        map.put("passWord","111");
        mapper.addUser2(map);
        sqlSession.commit();
        sqlSession.close();
    }

Map传递参数，直接在sql中取出key即可！----parameterType="map"
对象传递参数，直接在sql中取对象的属性即可！----parameterType="com.god.pojo.User"/parameterType="object"
只有一个基本类型参数的情况下，可以直接在sql中取到！
多个参数用map，或者注解！

8、模糊查询

1、Java代码执行的时候，传递通配符% %
2、在sql拼接中使用通配符

 //模糊查询
    List <User> getUserLike(String value);

  <!--模糊查询-->
    <select id="getUserLike" resultType="com.god.pojo.User">
        select * from user where name like #{value}
        //select * from user where name like "%"#{value}"%"
    </select>

    @Test
    public void getUserLike() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserLike("%迦%");
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }