PDO_locks version

pdo_transactions_locks.php

function is_course_available($id_course) {
    $sql = "SELECT id_course FROM students_courses WHERE id_course = $id_course";
    $statement = Connection::get_connection()->query($sql);
    $students_course = $statement->fetchAll();
    return count($students_course) < MAX_NUMBER_OF_STUDENTS_PER_COURSE;
}

function insert_student_course($id_student, $id_course) {
    $sql = "INSERT INTO students_courses(id_student, id_course) VALUES($id_student, $id_course)";
    $statement = Connection::get_connection()->prepare($sql);
    $statement->execute();
}


$student = get_random_student();
$course = get_random_course();

Connection::get_connection()->beginTransaction();

Connection::get_connection()->query("LOCK TABLE students_courses");

if (! is_course_available($course['id'])) {
    Connection::get_connection()->rollBack();
    echo "Not avaialble.\n";
    exit;
}

insert_student_course($student['id'], $course['id']);
Connection::get_connection()->commit();
echo "Registered.\n";