Prevent timeslot from being double booked

Question

I have a calendar where I can pick a date, and then a table of timeslots will appear. In the table I can either see information about the user who has booked the timeslot, or click a reserve link.

To display the information, I check select all records from my booking table where the room id is equal to the current room that I am booking for, the eventdate, that is equal to the date that I clicked in the calender and the timeslot which it equal to the timeslot that I clicked on:

$sql = "SELECT * FROM bookings WHERE room_id= '" . $room_id . "' AND eventDate='" . $dateToCompare . "'AND timeslot = $time;";
$result = $db->mysqli->query ( $sql );

    if (mysqli_num_rows ( $result ) == 0) {
        echo "<a href='" . $_SERVER ['PHP_SELF'] . "?id=" . $room_id . "&month=" . $month . "&day=" . $day . "&year=" . $year . "&t={$time}&v=true&f=true&reserved=true'><h3 style='color: rgb(255,0,0);'>Reserve</h3></a>";
    } 

    else {  .... }

As you can see I set put reserved=true in my Reserve link, and by calling that I insert into my database.

if (isset ( $_GET ['reserved'] )) {
    $sqlreserve = "INSERT INTO bookings (user_id, room_id, eventDate, timeslot) VALUES ('" . $user_id . "','" . $room_id . "','" . $dateToCompare . "','" . intval ( $_GET ['t'] ) . "');";
    $resultreserve = $db->mysqli->query ( $sqlreserve );
    echo $resultreserve;
}

I would end up with a link looking something like this:

mysite.php/id=2&month=04&day=23&year=2014&t=12&v=true&f=true&reserved=true

However, this is where I have my problem. If I refresh my page, a booking will be made again. I'm a bit lost on what the solution would be, and that is why I'm asking you guys.

How can a restrick a specific timeslot on a specific day, to only be booked once?

A booking would look like this in my database:

user_id - room_id - eventDate - timeslot
28        3         04/18/2014  8

The eventdate and the timeslot should not be UNIQUE separately. A time slot could have the value of 10, 200 times fx. But the eventdate and the timeslot should be UNIQUE togeather.

Is this possible?

EDIT:

I tried to add this:

ALTER TABLE `exam`.`bookings` ADD UNIQUE `idx_booking` (`eventDate`, `timeslot`);

And it almost works. However, I can't delete the timeslot that I reserved last. All of the others I can delete.

My delete looks like this:

if ($booking->deleteBooking($_GET['id']))
{
    header('Location: ' . $_SERVER['HTTP_REFERER']);
}
else
{
    echo "Could not delete the booking!";
}



public function deleteBooking($id)
    {
        $sql = "DELETE FROM bookings WHERE id = ?";
        if (!$result = $this->db->mysqli->prepare($sql))
        {
            return false;
        }

        if (!$result->bind_param('i', $id))
        {
            return false;
        }

        return $result->execute();
    }

I've found the error!

Each time I deleted the last booking, it wan't back and booked that timeslot again.

Answer 1

In the reservation script you must check again if the slot is free before you try to book it.

It can even happen that two people try to book the same slot at the same time. Only one of them should get the slot.

---

Additionally to ensure you are never double booked you could add a CONSTRAINT to your MySQL database.

CREATE UNIQUE INDEX `idx_booking` ON `bookings` (room_id, eventDate)

Now your INSERT query will fail if you try to book a room twice on the same date. This may or may not be desirable. Sometimes people stay for only a very short time so maybe you want to allow double bookings.

Answer 2

Place some conditional logic in your query that references booked or reserved status depending on this answer continue with your logic