Mybatis 动态SQL

mybatis-08

实体类

public interface BlogMapper {
    
    //查询博客
    List<Blog> queryBlogIF(Map map);

    List<Blog> queryBlogChoose(Map map);

    //更新博客
    int updateBlog(Map map);

　　List<Blog> queryBlogForeach(Map map);

}

动态SQL：

 <!-- 1.IF语句   每一个if都会按顺序执行 -->
    <!--  都要用where标签！！！安全  可以自动识别拼接的语句
            1.如果第一个语句的开始是and或者是or可以自动去除
            2.如何后面没有拼接语句 自己去除where  -->
    <select id="queryBlogIF" parameterType="map" resultType="Blog">
        select * from mybatis.blog
        <where>
            <if test="title!=null">
                title = #{title}
            </if>
            <if test="author!=null">
                and author =#{author}
            </if>
        </where>
    </select>

<!-- 2.choose(when,otherwise)   类似java中的switch  只会按循序执行成立就立即输出（只会成立其中一个）-->
    <select id="queryBlogChoose" parameterType="map" resultType="Blog">
        select * from mybatis.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>

 <!-- 3.set语句
            1.用于update会动态前置set关键字
            2.会自动删除无关的逗号
            3.记得拼接语句的时候有的加逗号-->
    <update id="updateBlog" parameterType="map">
        update mybatis.blog
        <set>
            <if test="title!=null">
                title =#{title},
            </if>
            <if test="author!=null">
                author=#{author}
            </if>
        </set>
        where id =#{id}
    </update>

<!-- 4.foreach   -->
    <select id="queryBlogForeach" parameterType="map" resultType="Blog">
        select * from blog
        <where>
            <foreach collection="ids" item="id" open="and (" close=")" separator="or">
                id = #{id}
            </foreach>
        </where>
    </select>

@Test
public void test05(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
    HashMap map = new HashMap<String,Object>();

    ArrayList<Integer> ids = new ArrayList<>();
    ids.add(1);
    ids.add(2);
    ids.add(3);
    map.put("ids",ids);
    List<Blog> blogs = mapper.queryBlogForeach(map);
    for (Blog blog:blogs) {
        System.out.println(blog);
    }
    sqlSession.close();
}