渚漪Day29——SSM【Mybatis06】

12、动态SQL

动态SQL就是指根据不同的调价生成不同的SQL语句

搭建环境

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

创建一个基础工程

1. 导包

2. 编写配置文件

3. 编写实体类

4. 编写对应的接口和xml

   <?xml version="1.0" encoding="UTF-8" ?>
   <!DOCTYPE mapper
           PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
           "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
   <mapper namespace="com.ijuy.dao.BlogMapper">
   
       <insert id="addBlog" parameterType="Blog">
           insert into mybatis.blog(id, title, author, create_time, views)
           values (#{id},#{title},#{author},#{createTime},#{views});
       </insert>
   
   </mapper>
   

import com.ijuy.dao.BlogMapper;
import com.ijuy.pojo.Blog;
import com.ijuy.util.IdUtils;
import com.ijuy.util.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.Date;

public class MyTest {
    @Test
    public void test1(){

        try(SqlSession sqlSession = MybatisUtils.getSqlSession()) {
            BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
            Blog blog = new Blog();
            blog.setId(IdUtils.getId());
            blog.setTitle("Mybatis");
            blog.setAuthor("狂神说");
            blog.setCreateTime(new Date());
            blog.setViews(9999);

            mapper.addBlog(blog);

            blog.setId(IdUtils.getId());
            blog.setTitle("Java");
            mapper.addBlog(blog);

            blog.setId(IdUtils.getId());
            blog.setTitle("Spring");
            mapper.addBlog(blog);

            blog.setId(IdUtils.getId());
            blog.setTitle("微服务");
            mapper.addBlog(blog);
        }
    }
}

IF

<select id="queryBlogIf" parameterType="map" resultType="blog">
    select * from mybatis.blog
    <where>
        <if test="title != null">
        and title=#{title}
    </if>
    <if test="author != null">
        and author=#{author}
    </if>
    </where>
</select>

choose

<select id="queryBlogChoose" parameterType="map" resultType="blog">
    select * from mybatis.blog
    <where>
        <choose>
            <when test="title!=null">
                title = #{title}
            </when>
            <when test="author!=null">
                author = #{author}
            </when>
            <otherwise>
                views=#{views}
            </otherwise>

        </choose>
    </where>
</select>

trim（where，set）

where：补充SQL中的where，自动去掉多余的and

set：补充SQL中的set，自动去掉，（逗号）

所谓的动态sql，本质上还是sql语句只是我们可以在sql层面，去执行一个逻辑代码

13、缓存【跳过】