单表查询操作
参数占位符#{}和${}
- #{}：相当于JDBC里面替换占位符的操作方式（#{}->“”）.相当于预编译处理（预编译处理可以防止SQL注入问题）
- ${}：相当于直接替换(desc这种关键字)，但这种不能预防SQL注入
select * from userinfo where username='${name}'
${} VS #{}
- ${}是直接替换，#{}是预执行；
- ${} 会存在SQL 注入问题，#{}不存在SQL注入问题
SQL 注入
UserInfo userInfo = userMapper.login("admin","' or 1='1");
mysql> select * from userinfo where username = 'admin' and password ='' or 1='1';
+----+----------+----------+-------+---------------------+---------------------+-------+
| id | username | password | photo | createtime | updatetime | state |
+----+----------+----------+-------+---------------------+---------------------+-------+
| 1 | admin | admin | | 2021-12-06 17:10:48 | 2021-12-06 17:10:48 | 1 |
+----+----------+----------+-------+---------------------+---------------------+-------+
1 row in set (0.00 sec)
like模糊查询
用concat进行字符串拼接
<select id="findListByName" resultMap="BaseMap">
select * from userinfo where username like concat('%',#{name},'%')
</select>
多表查询操作
一对一多表查询
一对一的多表查询：需要设置resultMap中有个association标签，property对应实体类的属性名，resultMap是关联属性的字典映射(必须要设置)，columnPrefix是设置前缀，当多表查询中有相同的字段的话，就会报错
<?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.example.demo.mapper.ArticleInfoMapper">
<resultMap id="BaseMap" type="com.example.demo.model.ArticleInfo">
<!--主键-->
<id property="id" column="id"></id>
<!--普通属性-->
<result property="updatetime" column="updatetime"></result>
<result property="title" column="title"></result>
<result property="content" column="content"></result>
<result property="createtime" column="createtime"></result>
<result property="rcount" column="rcount"></result>
<!--自定义对象属性-->
<association property="user"
resultMap="com.example.demo.mapper.UserMapper.BaseMap"
columnPrefix="u_">
</association>
</resultMap>
<select id="getAll" resultType="com.example.demo.model.ArticleInfo">
select a.*,u.id from articleinfo as a left join userinfo as u on a.uid = u.id;
</select>
<select id="getAll2" resultMap="BaseMap">
select a.*,u.id as u_id ,u.username as u_username,u.password as u_password from articleinfo as a left join userinfo as u on a.uid = u.id;
</select>
</mapper>
一对多多表查询
collection标签，用法同association
<resultMap id="BaseMapper2" type="com.example.demo.model.UserInfo">
<!--映射主键的）（表中主键和程序实体类中的主键）-->
<id column="id" property="id"></id>
<!--普通列的映射-->
<result column="username" property="name"></result>
<result column="password" property="password"></result>
<result column="photo" property="photo"></result>
<result column="createtime" property="createtime"></result>
<result column="updatetime" property="updatetime"></result>
<!--外部关联-->
<collection property="artlist" resultMap="com.example.demo.mapper.ArticleInfoMapper.BaseMap"
columnPrefix="a_"></collection>
</resultMap>
<select id="getAll3" resultMap="BaseMapper2">
select u.*,a.id a_id,a.title a_title from userinfo u left join articleinfo a on u.id=a.uid
</select>
动态SQL使用
if标签
注册分为必填和选填，如果在添加用户的时候有不确定的字段传入，就需要使用动态标签if来判断
//p是传递过来的参数名，并不是表的字段名
<insert id="add3">
insert into userinfo(username,password,
<if test="p!=null">
photo,
</if>
state)
values(#{username},#{password},
<if test="p!=null">
#{p},
</if>
#{state})
</insert>
trim标签
trim标签的属性
- prefix：表示整个语句块，以prefix的值作为前缀
- suffix：表示整个语句块，以suffix的值作为后缀
- prefixOverrides：去掉最前面的符合条件的字符
- suffixOverrides：去掉最后面的符合条件的字符
<insert id="add4">
insert into userinfo
<trim prefix="(" suffix=")" suffixOverrides=",">
<if test="username!=null">
username,
</if>
<if test="password!=null">
password,
</if>
<if test="p!=null">
photo,
</if>
<if test="state!=null">
state,
</if>
</trim>
values
<trim prefix="(" suffix=")" suffixOverrides=",">
<if test="username!=null">
#{username},
</if>
<if test="password!=null">
#{password},
</if>
<if test="p!=null">
#{p},
</if>
<if test="state!=null">
#{state},
</if>
</trim>
</insert>
where标签
where标签首先可以帮助我们生成where，如果有查询条件，那么就生成where，如果没有查询条件，就会忽略where
其次where标签可以判断第一个查询条件前面有没有and，如果有则会删除
<select id="login2" resultType="com.example.demo.model.UserInfo">
select * from userinfo
<where>
<if test="username!=null">
username=#{username}
</if>
<if test="password!=null">
and password=#{password}
</if>
</where>
</select>
set标签
和where的使用基本一样
可以自动帮助你处理最后一个逗号，并且自动写set
<update id="update" parameterType="map">
update blog
<set>
<if test="newTitle != null">
title=#{newTitle},
</if>
<if test="newAuthor != null">
author=#{newAuthor},
</if>
<if test="newViews != null">
views = #{newViews}
</if>
</set>
<where>
<if test="id != null">
id=#{id}
</if>
<if test="title != null">
and title=#{title}
</if>
<if test="author != null">
and author=#{author}
</if>
<if test="views != null">
and views = #{views}
</if>
</where>
</update>foreach标签
- foreach属性：
- collection：参数集合的名字
- item：给接下来要遍历的集合起的名字
- open：加的前缀是什么
- close：加的后缀是什么
- separator：每次遍历之间间隔的字符串
<delete id="dels">
delete from userinfo where id in
<foreach collection="list" item="item" open="(" close=")" separator="," >
#{item}
</foreach>
</delete>
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