Hide/Show button, also when refreshed - php

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

Answer 2

// First you need to get all the activityIDs from the table where you want to search and put them into an array
$sql2 = "SELECT * FROM user_activity";
$stm2 = $db->prepare($sql2);
$result2 = $stm2->execute(array());
$user_activityID = array();
while($row2 = $stm->fetch(PDO::FETCH_ASSOC))
{
// if in the table user_activity the column you are trying to compare has the same name as in activity -- $row2['ActivityID']
array_push($row2['ActivityID'], $user_activityID);
}
// Then you use in_array to compare while you go through the user_activity table
$sql = "SELECT * FROM activity";
$stm = $db->prepare($sql);
$result = $stm->execute(array());
while($row = $stm->fetch(PDO::FETCH_ASSOC))
{
if (in_array($row['ActivityID'], $user_activityID))
{
// yes the current $row['ActivityID'] from the activity table, exists in the user_activity table
// you can choose whether or not to add this to your array
array_push($row['ActivityID'], $activityID);
}
}
I'm sure there's other more efficient ways to do this, using some pdo stuff that I don't know, but this is how I would have done it.