src/main/resources/mapper/CommentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.pt5.pthouduan.mapper.CommentMapper">

    <!-- 创建评论 -->
    <insert id="save" parameterType="com.pt5.pthouduan.entity.Comment">
        INSERT INTO comment (commentid, userid, postid, post_commentcontent, commenttime)
        VALUES (#{commentid}, #{userid}, #{postid}, #{postCommentcontent}, #{commenttime})
    </insert>

    <!-- 删除评论 -->
    <delete id="deleteByCommentid" parameterType="int">
        DELETE FROM comment WHERE commentid = #{commentid}
    </delete>

    <!-- 更新评论 -->
    <update id="updateComment" parameterType="com.pt5.pthouduan.entity.Comment">
        UPDATE comment
        SET userid = #{userid},
            postid = #{postid},
            post_commentcontent = #{postCommentcontent},
            commenttime = #{commenttime}
        WHERE commentid = #{commentid}
    </update>

    <!-- 按帖子ID查询所有评论 -->
    <select id="selectByPostid" parameterType="int" resultType="com.pt5.pthouduan.entity.Comment">
        SELECT * FROM comment
        WHERE postid = #{postid}
        ORDER BY commenttime ASC
    </select>

    <!-- 点赞 +1 -->
    <update id="incrementLikes" parameterType="int">
        UPDATE comment
        SET likes = likes + 1
        WHERE commentid = #{commentid}
    </update>

    <!-- 取消点赞 -1（最小为0） -->
    <update id="decrementLikes" parameterType="int">
        UPDATE comment
        SET likes = CASE
                        WHEN likes > 0 THEN likes - 1
                        ELSE 0
            END
        WHERE commentid = #{commentid}
    </update>


</mapper>