Mybatis之动态SQL(choose、when、otherwise)

上篇以及学习了动态sql的if用法，这里学习choose、when、otherwise的用法。

先介绍<where>标签的用法：

where 元素只会在子元素返回任何内容的情况下才插入 “WHERE” 子句。而且，若子句的开头为 “AND” 或 “OR”，where 元素也会将它们去除。

这里直接上mapper.xml代码

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

测试类

@Test
    public void queryBlogChooseTest(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
        HashMap map = new HashMap();
        map.put("author","狂神说");
        map.put("title","Mybatis");
        mapper.queryBlogChoose(map);
        sqlSession.commit();
        sqlSession.close();
    }
           

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增加set用法

<update id="queryBlogInsert" parameterType="map">
        update mybatis.blog
        <set>
            <if test="title != null">
                title = #{title},
            </if>
            <if test="author != null">
                author = #{author},
            </if>
            <if test="views != null">
                views = #{views},
            </if>
        </set>
        where id = #{id}
    </update>