1.namespace

namespace 中的 类名要与Dao包下的接口名一致，且为全限定名

2.select insert update delete标签参数

• id:就是对应的namespace中的方法名
• resultType：sql语句的返回值
• 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">
<mapper namespace="com.sun.dao.UserDao">
    <select id="getUserList" resultType="com.sun.pojo.User">
        select * from user
    </select>

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

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

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

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

3.Dao层

package com.sun.dao;

import com.sun.pojo.User;

import java.util.List;

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

    User getUserById(int id);

    int addUser(User user);

    int updateUser(User user);

    int deleteUser(int id);
}

4.测试

package com.sun.dao;

import com.sun.pojo.User;
import com.sun.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

public class UserDaoTest {
    @Test
    public void test(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        for (User user : mapper.getUserList()) {
            System.out.println(user);
        }
        sqlSession.close();
    }

    @Test
    public void test1(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        User user = mapper.getUserById(2);
        System.out.println(user);
        sqlSession.close();
    }

    @Test
    public void test3(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        User user = new User(5,"ceshi","asdsadasd");
        int i = mapper.addUser(user);
        sqlSession.commit();
        if(i>0){
            System.out.println("增加成功");
        }
        sqlSession.close();
    }

    @Test
    public void test4(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        User user = new User(5,"ceshi","55555555555555");
        int i = mapper.updateUser(user);
        sqlSession.commit();
        if(i>0){
            System.out.println("修改成功");
        }
        sqlSession.close();
    }

    @Test
    public void test5(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        int i = mapper.deleteUser(5);
        sqlSession.commit();
        if(i>0){
            System.out.println("删除成功");
        }
        sqlSession.close();
    }
}

注意修改数据库是提交事务

5.错误排查

• 标签不要匹配错
• resource绑定Mapper文件，需要使用路径
• 程序配置文件必须符合规范
• 空指针异常，没有注册到资源
• 输出文件中文乱码问题
  idea配置中文编码
• maven资源没有导出

6.Map标签

int addUser2(Map<String,Object> map);

<insert id="addUser2" parameterType="Map">
        insert into user(name,pwd) values (#{username },#{userpwd })
</insert>

@Test
    public void test5(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("username","撒点娇阿萨德拉萨家里卡上");
        map.put("userpwd","kkkkkkkkkkkk");
        int i = mapper.addUser2(map);
        if(i>0){
            System.out.println("添加成功");
        }
        sqlSession.commit();
        sqlSession.close();
    }

map可以替代类型，万能的map,xml中进行赋值时，为map的key值

7.resultMap

<!-- 解决数据库字段与实体属性不一致的问题 -->
    <resultMap id="userMap" type="User">
        <result column="id" property="id"/>
        <result column="name" property="name"/>
        <result column="pwd" property="pwd"/>
    </resultMap>

• resultMap 元素是MyBatis中最重要的最强大的元素
• resultMap 的设计思想是，对于简单的语句根本不需要配置显式的结果映射，而对于复杂一点的语句只需要描述它们的关系就行了
• resultMap 最优秀的地方在于，虽然你已经对它相当了解了，但是根本就不需要显式的用到它们
• 如果世界总是这么简单就好了

8.日志

如果一个数据库操作，出现了异常，我们需要排错，日志就是最好的助手
曾经：sout,debug
现在：日志工厂

<settings>
    <setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>

image.png

9.分页

思考：为什么分页？

• 减少数据的处理量
  limit分页

语法：select * from user limit startIndex,pageSize   //startIndex 为开始条数，pageSize 每页多少条数据
select * from user limit 3  [0,n]

List<User> getUserByLimit(Map<String,Integer> map);

<select id="getUserByLimit" parameterType="map" resultType="User">
      select * from user limit #{startIndex},#{pageSize}
</select>

//测试
@Test
    public void testLimit(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        HashMap<String, Integer> map = new HashMap<String, Integer>();
        map.put("startIndex",0);
        map.put("pageSize",2);
        for (User user : mapper.getUserByLimit(map)) {
            System.out.println(user);
        }
        sqlSession.close();
    }

github地址：https://github.com/sunmaio159/mybatis-study