Question

I am making an application that displays “activities”. Each activity has his own button. When you click on that button, you add that specific activity to your “guide”. The idea is that you can add one specific activity only once, so the button of that activity must disapear when it’s added to the guide. I can use a simple $(this).hide() in my javascript but that obviously doesn’t work when I refresh the page. So I guess i should make a check if the activity exists in de guide.

in the database I have 3 tables, 1: activity (with an ActivityID), 2: user (with a UserID) and 3: user_activity (with ActivityID and UserID, a linktable).

So the check must check if the ActivityID exists in the user_activity table, and that the UserID that belongs to that ActivityID in the user_activity table is the sames as the current users’ ID.

At this moment, I know how to check the current users UserID:

//userid
$sql = "SELECT * FROM user WHERE Username = '".$_SESSION['Username']."' ";
$stm = $db->prepare($sql);
$result = $stm->execute(array());
while($row = $stm->fetch(PDO::FETCH_ASSOC)) {
$userid = $row['UserID'];
}

But I don’t know how to check if the ActivityID already exists, and how I should make this
if else statement.

Ay the moment I use this script to display the activity (incl. the button)

$sql = "SELECT * FROM activity";
$stm = $db->prepare($sql);
$result = $stm->execute(array());   

while($row = $stm->fetch(PDO::FETCH_ASSOC))
{
    echo '<div id="activity'.$row['ActivityID'].'">';
    echo '<img src="data:image/jpeg;base64,' . base64_encode( $row['ActivityIMG'] ) . '" >', '<br>';
    $instantguide = $row['ActivityID'];
    echo '<input type="button" class="addActivity" onclick="MakeRequest(' . $instantguide . ')" value="Activiteit toevoegen" data-activity="' . $row['ActivityID'] . '">';
    echo '</div>';
}

Answer 1

You need a LEFT JOIN to see what activities are already on

SELECT a.*, ua.ActivityID as added 
FROM activities a LEFT JOIN user_activity ua 
    ON a.ActivityID=ua.ActivityID AND UserID=:userid

So you’ll have an additional added field in the resultset, filled with an id if it is already chosen or empty otherwise