isset function submits all buttons inside the while loop PHP

Question

im having this problem where the submit button inside the while loop re-execute the while loop.

PHP:

$query1 = $con->query("SELECT * FROM room");
if($query1->num_rows > 0) {
    while($row1 = $query1->fetch_array()) {
        $idroom = $row1['idroom'];

        echo "<tr>";
        echo "<td> $idroom </td>";
        echo "<td> <form method='POST'> <input type='submit' name='delete' value='DELETE'> </form></td>";
        echo "</tr>";

        if(isset($_POST['delete'])) {
            $query2 = $con->query("DELETE FROM room WHERE idroom='$idroom'");
        }
    }
}

the table: [1]: https://i.stack.imgur.com/dujps.png

the problem is, when i click the delete button, it just deletes all of the room INSTEAD OF the room that i want to delete. i believe the program thinks that i presses all of the delete button at once because of the 'isset' function.

things that ive tried:

• replacing the $query2 line inside isset with echo $idroom; and the output is room1room2room3 . which means the program thinks that i presses all of the buttons at once.

Answer 1

There are lots of things wrong with this code, not least that it is incredibly insecure and vulnerable to injection. You should read about prepared statements before you go any further. There are no end of tutorials and SO answers for this so I won't cover them here. In the interests of helping out a new programmer (I was new not that long ago) I will point out what I believe is going wrong here:

1. $query1 = $con->query("SELECT * FROM room");

This is run every time the script runs. This is a key thing to realise. If you load the page, or if you submit a post delete this always happens. Which leads to:

2. if($query1->num_rows > 0) { while($row1 = $query1->fetch_array()) {...

You start your loop, looping through every record. Notice the every .

So for every single record, you then check:

3. if(isset($_POST['delete'])) {...

This is where your records are removed and what CBroe was pointing towards in his comment. You believe (I think) that you check for the deletion of this individual record however you only check isset($_POST['delete']) and you do this for EVERY record. Remember, the POST variable exists until the end of the script or until removed. So by clicking delete, and submitting that _POST value you pass this condition for every record in your loop.

• You should digest this for a little while before going further, as it's a common mistake with new programmers. Remember that the computer reads and actions the script in order, remember it also does EXACTLY what you ask it, and nothing more or less. The classic example is to describe making a cup of coffee. If i say to you 'put the kettle on, put coffee in the cup, fill up with water, add milk' you will make a coffee, but if you say that to a computer you will end up, at best with a computer wearing a kettle looking for a cup to put coffee in and telling you milk is not a number.

So the solution. Well I'm not going to write it for you, there are different options. You should be passing some kind of identifier to the the post that is specific to the record you want, and then you need to check that eg isset POST[delete] && isset(POST['room_id']) . Then you need to decide the best place to be doing it, at the start of the script, in a different script, probably not inside a loop (that's rarely a sign of great programming). If you are going to remove a record you should probably be doing it before you create output for it. (why collect a record just to then delete it, is that efficient?).

If you really must do it inside a loop then you need some kind of check that the id of the room is the same as the id of the post value before you run the delete.

Hopefully that is helpful, but ensure you look into and start using prepared statements as a matter of urgency - there's really no excuse not to do so in 2020

Answer 2

In your code, you didn't follow the basic structure. Use JS for the click event of edit/delete and use ajax call for actions to perform.

Here is one solution for your code based on your paste, It's not standard code but helps you to solve the issue.

$query1 = $con->query("SELECT * FROM room");
if($query1->num_rows > 0) {
    while($row1 = $query1->fetch_array()) {
        $idroom = $row1['idroom'];

        $tr = "<tr>";
        $tr .= "<td> $idroom </td>";
        $tr .= "<td><form method='POST'>";
        $tr .= "<input type='hidden' name='room_id' value='".$idroom."'>";
        $tr .= "<input type='submit' name='delete' value='DELETE'> </form></td>";
        $tr .= "</tr>";

        echo $tr;
    }
}

if(isset($_POST['delete'])) {
  $roomId = $_POST['room_id'];
  $query2 = $con->query("DELETE FROM room WHERE idroom='$roomId'");
}