Can anyone please help me where i am doing wrong ?

<?php


class DbFoodFunctions {

	private $conn;
	private function openDB() {

		$servername = "localhost";
		$username = "root";
		$password = "";
		$dbname = "blood";
		$this -> conn = new mysqli($servername, $username, $password, $dbname);
		if ($this -> conn -> connect_error) {
			die("Connection failed: " . $conn -> connect_error);
		}

	}

	private function closeDB() {
		$this -> conn -> close();
	}
	
	
	public function searchFood($money)
	{
		$this -> openDB();
		$stmt = $this -> conn -> prepare("Select * from FOOD where amount >= ?"); 
		$stmt -> bind_param("i", $money);
		$stmt -> execute();
		$result = $stmt -> get_result();
		$numrows = $result -> num_rows;
		$this -> closeDB();
		$res = array();
		$res['numrows'] = $numrows;
		while ($myrow = $result -> fetch_object()) {
			$res[] = $myrow;

		}
		return $res;
	}
	
}
?>

<?php

require_once 'db/db.php';

$dbObj = new DbFoodFunctions();
$action = '';
$result = array();

if ($action == 'searchFood') {
	$money = '';
		if (isset($_REQUEST['money'])) {
			$money = trim($_REQUEST['money']);
		}
		$res = $dbObj -> searchFood($money);
		$result['success'] = 1;
		$result['data'] = $res;
		echo json_encode($result);
}else {
	$result['error'] = 1;
	$result['message'] = "You are not authorized";
	echo json_encode($result);
}
?