MyBatis06——动态SQL
动态SQL
- if
- choose (when, otherwise)
- trim (where, set)
- foreach
搭建环境
1、搭建数据库
CREATE TABLE `blog` (
`id` varchar(50) NOT NULL COMMENT '博客id',
`title` varchar(100) NOT NULL COMMENT '博客标题',
`author` varchar(30) NOT NULL COMMENT '博客作者',
`create_time` datetime NOT NULL COMMENT '创建时间',
`views` int(30) NOT NULL COMMENT '浏览量'
) ENGINE=InnoDB DEFAULT CHARSET=utf8
2、实体类编写
@Data
public class Blog {
private String id;
private String title;
private String author;
private Date createTime;
private int views;
//set,get....
}
3、编写Mapper接口以及xml文件
public interface BlogMapper {
}
<?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.kuang.mapper.BlogMapper">
</mapper>
4、在setting中开启驼峰自动转换
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
<setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>
<!--注册Mapper.xml-->
<mappers>
<mapper resource="mapper/BlogMapper.xml"/>
</mappers>
5、插入初始数据
编写接口
//新增一个博客
int addBlog(Blog blog);
sql配置文件
<insert id="addBlog" parameterType="blog">
insert into blog (id, title, author, create_time, views)
values (#{id},#{title},#{author},#{createTime},#{views});
</insert>
IF语句
select * from blog where title = #{title} and author = #{author}
-->
<select id="queryBlogIf" parameterType="map" resultType="blog">
select * from blog where
<if test="title != null">
title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</select>
where语句
<select id="queryBlogIf" parameterType="map" resultType="blog">
select * from blog
<where>
<if test="title != null">
title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</where>
</select>
这个“where”标签会知道如果它包含的标签中有返回值的话,它就插入一个‘where’。此外,如果标签返回的内容是以AND 或OR 开头的,则它会剔除掉。
set语句
<!--注意set是用的逗号隔开-->
<update id="updateBlog" parameterType="map">
update blog
<set>
<if test="title != null">
title = #{title},
</if>
<if test="author != null">
author = #{author}
</if>
</set>
where id = #{id};
</update>
choose语句
<select id="queryBlogChoose" parameterType="map" resultType="blog">
select * from blog
<where>
<choose>
<when test="title != null">
title = #{title}
</when>
<when test="author != null">
and author = #{author}
</when>
<otherwise>
and views = #{views}
</otherwise>
</choose>
</where>
</select>
SQL片段
<sql id="if-title-author">
<if test="title != null">
title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</sql>
引用SQL片段
<select id="queryBlogIf" parameterType="map" resultType="blog">
select * from blog
<where>
<!-- 引用 sql 片段,如果refid 指定的不在本文件中,那么需要在前面加上 namespace -->
<include refid="if-title-author"></include>
<!-- 在这里还可以引用其他的 sql 片段 -->
</where>
</select>
Foreach
批量查询
1、编写接口
//批量查询
List<Blog> queryBlogForeach(Map map);
2、编写SQL语句
<select id="queryBlogForeach" parameterType="map" resultType="blog">
select * from blog
<where>
<!--
collection:指定输入对象中的集合属性
item:每次遍历生成的对象
open:开始遍历时的拼接字符串
close:结束时拼接的字符串
separator:遍历对象之间需要拼接的字符串
select * from blog where 1=1 and (id=1 or id=2 or id=3)
-->
<foreach collection="ids" item="id" open="and (" close=")" separator="or">
id=#{id}
</foreach>
</where>
</select>
批量插入
1、编写接口
int addUserForeach(@Param("list") List<Map> list);
2、编写SQL语句
<!-- 批量插入信息-->
<insert id="addUserForeach" parameterType="list">
insert into user
(id,name,pwd)
values
<foreach collection="list" item="user" separator=",">
(
#{user.id},
#{user.name},
#{user.pwd}
)
</foreach>
</insert>
posted on 2021-04-13 16:46 JavaCoderPan 阅读(10) 评论(0) 编辑 收藏 举报 来源