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Mybatis动态SQL

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单表查询操作

参数占位符#{}和${}

select * from userinfo where username='${name}'

${} VS #{}

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

 <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

 <delete id="dels">
        delete from userinfo where id in
        <foreach collection="list" item="item" open="(" close=")" separator="," >
            #{item}
        </foreach>
 </delete>

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