Question

I am using the below code to insert ratings for specific songs on my application.

I am recording the songID, the rating given to the song and the userID who has voted on the song.

What I want to do is to prevent a user from voting if they have ‘already’ voted on a specific song. Therefore I need to be able to check if a row exists in the table before insertion.

So… If userID = 1, songID = 1 and rating = 4. This should insert fine.

If subsequently, an insertion attempt is made for userID=1, songID=1, rating=*, it should fail to insert

However if the user is voting on a different song… that should be allowed and the insertion should happen.

Any ideas how I would go about this?

//Add rating to database

if(!empty($_POST['rating']) && isset($_POST))
{
    //make variables safe to insert
  $rating = mysql_real_escape_string($_POST['rating']);
  $songid = mysql_real_escape_string($_POST['song_id']);

    //query to insert data into table
    $sql = "
        INSERT INTO wp_song_ratings
        SET
        songid = '$songid',
        rating = '$rating',
        userid = '$user_id'";
    $result = mysql_query($sql);
    if(!$result)
    {
        echo "Failed to insert record";
    }
    else
    {
        echo "Record inserted successfully";
    }
}

Answer 1

Add a UNIQUE KEY for userID and songID. If you don’t want them to change their rating you shouldn’t allow it from the front-end, but still make the check on the backend. It will fail if a UNIQUE KEY is in place.

ALTER TABLE `wp_song_ratings` ADD UNIQUE KEY `user_song_key` (`userID`, `songID`)