myBatis(sql片段)

//将片段提取出来，命名后，在引用的地方用<include refid=""></include>
    <sql id="if">
            <if test="title != null">
                and title =#{title}
            </if>
            <if test="author != null">
                and author=#{author}
            </if>
    </sql>

    <!--某列的if模糊查询，全部if都会判断-->
    <select id="QueryBlog" resultType="pojo.Blog" parameterType="map">
        select * from myBatis.blog
<where>
    <include refid="if"></include>
</where>
    </select>

注意

1. 最好基于单表的操作
2. 不要存在where标签，where标签会修改片段符号

foreache

blogMapper.xml

    <select id="QueryBogForeach" resultType="pojo.Blog" parameterType="map">
        /* select * from myBatis.blog where id in(1 ,2 ,3)*/
        select * from myBatis.blog
        <where>
        <foreach collection="ids" item="IID" open="id in (" close=")" separator=",">
          /*这里内容是每一个IID，IID是ids集合的每一项元素，需要往ids集合填充元素*/
            #{IID}
        </foreach>
        </where>
    </select>

测试

 @org.junit.Test
    public void QueryBogForeach() {
        SqlSession sqlSession = myBatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        Map<String, Object> map = new HashMap<>();

        //创建一个集合填充ids的集合
        ArrayList<Integer> IDs = new ArrayList<>();
        map.put("ids", IDs);
        IDs.add(1);

        List<Blog> blogs = mapper.QueryBogForeach(map);
        for (Blog blogg : blogs) {
            System.out.println(blogg);
        }
        sqlSession.close();
    }