php - 允许用户在 PHP 中投票一次

Question

我正在做一个学校项目，我需要允许用户对图片进行投票。用户可以将图片向上或向下。他们可以随时更改投票，但不能撤消投票，因此一旦他们投票，要么赞成，要么反对。

我一直在尝试一些事情，但我似乎无法让它发挥作用。它在用户第一次按下赞成票时起作用，然后用户可以将他的投票改为反对票。但是当他再次尝试投票时，什么也没有发生，这已经困扰我一段时间了，我将不胜感激任何帮助。

到目前为止，这是我的代码:

 if (isset($_SESSION['loggedin'])) {
    $result = mysql_query("SELECT * FROM user2pics WHERE picid = $id AND userid = $user");
    if (mysql_num_rows($result) == 0) {
        $votes_up = $cur_votes[0] + 1;
        $resultaat = mysql_query("UPDATE pics SET likes = $votes_up WHERE picid = $id");
        if ($resultaat) {
            $query = mysql_query("INSERT INTO user2pics (picid, userid, vote) VALUES ($id, $user, 1)");
            if ($query) {
                $effectiveVote = getEffectiveVotes($id);
                echo $effectiveVote . " votes";
            } elseif (!$query) {
                echo "Failed!";
            }
        } elseif (!$resultaat) {
            echo "Failed insert in pics!";
        }
    } else {
        $row = mysql_fetch_array($result);
        if ($row['vote'] == 0) {
            $votes_down = $cur_votes[0] + 1;
            $result = mysql_query("UPDATE pics SET likes = $votes_up WHERE picid = $id");
            if ($result) {
                $resultaat = $mysqli -> prepare("UPDATE user2pics SET vote = 1 WHERE picid = $id AND userid = $user");
                $resultaat -> execute();
                $effectiveVote = getEffectiveVotes($id);
                if ($resultaat -> affected_rows == 1) {
                    echo $effectiveVote . " votes";
                }
            }
        } else {
            $effectiveVote = getEffectiveVotes($id);
            echo $effectiveVote . " votes";
        }
    }
} else {
    echo "Please login first!";
}
} elseif ($action == 'vote_down'){
if (isset($_SESSION['loggedin'])) {
    $result = mysql_query("SELECT * FROM user2pics WHERE picid = $id AND userid = $user");
    if (mysql_num_rows($result) == 0) {
        $votes_down = $cur_votes[1] + 1;
        $resultaat = mysql_query("UPDATE pics SET dislikes = $votes_down WHERE picid = $id");
        if ($resultaat) {
            $query = mysql_query("INSERT INTO user2pics (picid, userid, vote) VALUES ($id, $user, 0)");
            if ($query) {
                $effectiveVote = getEffectiveVotes($id);
                echo $effectiveVote . " votes";
            } elseif (!$query) {
                echo "Failed to dislike!";
            }
        } elseif (!$resultaat) {
            echo "Failed insert in pics!";
        }
    } else {
        $row = mysql_fetch_array($result);
        if ($row['vote'] == 1) {
            $votes_down = $cur_votes[1] + 1;
            $result = mysql_query("UPDATE pics SET dislikes = $votes_down WHERE picid = $id");
            if ($result) {
                $resultaat = $mysqli -> prepare("UPDATE user2pics SET vote = 0 WHERE picid = $id AND userid = $user");
                $resultaat -> execute();
                $effectiveVote = getEffectiveVotes($id);
                if ($resultaat -> affected_rows == 1) {
                    echo $effectiveVote . " votes";
                }
            }
        } else {
            $effectiveVote = getEffectiveVotes($id);
            echo $effectiveVote . " votes";
        }
    }
} else {
    echo "Please login first!";
}
}

$cur_votes 定义为:$cur_votes = getAllVotes($id);

function getAllVotes($id) {
$votes = array();
$q = "SELECT * FROM pics WHERE picid = $id";
$r = mysql_query($q);
if (mysql_num_rows($r) == 1)//id found in the table
{
    $row = mysql_fetch_assoc($r);
    $votes[0] = $row['likes'];
    $votes[1] = $row['dislikes'];
}
return $votes;
}

function getEffectiveVotes($id) {
/**
 Returns an integer
 **/
$votes = getAllVotes($id);
$effectiveVote = $votes[0] - $votes[1];
return $effectiveVote;
}

Answer 1

您通过在两个地方存储“喜欢”来复制功能。

我没有查看您的弱实体(用户和投票表)，所以我们假设它将包含三个字段:user_id、item_id 和 vote TINYINT。 user_id 和 item_id 上的主键，因此同一用户只能对每个项目投一票。

根据赞成或反对将投票设置为 1 或 -1，而不是将 likes 存储在项目表中，像这样动态计算项目的总票数:

SELECT SUM(vote) FROM user_votes WHERE item_id = ?;

如果您只想要赞成票，请执行以下操作:

SELECT SUM(vote) FROM user_votes WHERE item_id = ? AND vote = 1;

当用户想要记录或更改他的投票时，您可以使用 REPLACE INTO 语法(感谢 Anigel 的建议——我完全错过了)来存储用户的新投票:

REPLACE INTO user_votes (user_id, item_id, vote) VALUES (?, ?, ?);