if(isset($_POST["submit"])){
//$hostname='localhost';
//$username='root';
//$password='';


try {
    $dbh = new PDO("mysql:host=$hostname;dbname=college",$username,$password);

    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $sql = "INSERT INTO students (student_name, student_email, student_city)
    VALUES ('".$_POST["stu_name"]."','".$_POST["stu_email"]."','".$_POST["stu_city"]."')";
    if ($conn->query($sql)){
        echo "<script type= 'text/javascript'>alert('New Record Inserted Successfully');</script>";
    }
    else{
        echo "<script type= 'text/javascript'>alert('Data not successfully Inserted.');</script>";
    }

    $dbh = null;
    }
catch(PDOException $e)
{
    echo $e->getMessage();
    }

}

require_once('../config/database.php'); //file with connection to db

class Category {
...
public function create() {
   ???
}

class Database {

public function getConnection() {
    $servername = "localhost";
    $username = "root";
    $password = "";
    try {
        $conn = new PDO("mysql:host=$servername;dbname=demo", $username, $password);
        // set the PDO error mode to exception
        $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        echo "Connected successfully with the database!<br/><br/>";
        return $conn;

    } catch (PDOException $e) {
        echo "Connection failed with the database!<br/><br/> " . $e->getMessage();
    }

}

}

$db = new Database();
$conn = $db->getConnection();


?>