Dynamic SQL-(Sql fragment and Foreach traversal)

Dynamic SQL is splicing SQL statements, as long as we ensure the correctness of SQL, we can arrange and combine them according to the format of SQL.

Following the previous article https://blog.csdn.net/m0_74135466/article/details/127997864?spm=1001.2014.3001.5501

//    SQL片段
    List<Blog> queryBlogIF1(Map map);

<!--    SQl片段
            将一部分公共的Sql语句抽取出来放在<sql id=" ">标签中，
            然后在需要使用SQL的地方使用include标签引用即可-->
    <sql id="if-title-author">
        <if test="title != null">
             title = #{title}
        </if>
        <if test="author != null">
            and author = #{author}
        </if>
    </sql>
    <select id="queryBlogIF1" parameterType="map" resultType="blog">
        select *from mybatis.blog where
        <include refid="if-title-author"></include>
    </select>
<!--    注意：
            1.最好基于单表来定义SQL片段
            2.SQL标签内不要存在WHERE标签-->

 Foreach:

//    查询1-2-3 号记录的博客
    List<Blog> queryBlogForeach(Map map);
}

<!--    Foreach-->
<!--    传递一个map,map中可以存在一个集合-->
<select id="queryBlogForeach" parameterType="map" resultType="blog">
    select *from mybatis.blog
<where>
    <foreach collection="ids" item="id" open= "and (" close =")" separator="or">
        id = #{id}
    </foreach>
</where>

</select>

@Test
    public void queryBlogforeach(){
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
        HashMap map = new HashMap();
        ArrayList<Integer> ids = new ArrayList<Integer>();
        ids.add(1);
//        ids.add(2);
        map.put("ids",ids);
        List<Blog> blogs = mapper.queryBlogForeach(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }

        sqlSession.close();
    }