Small DB class

<?php

/**
 * Generic database connection class
 *
 * Required: PHP 5.6
 * Based on: https://codeshack.io/super-fast-php-mysql-database-class/
 *
 * Example usage:
 *  include_once("db.php");
 *  $this->db = new DB($dbhost, $dbuser, $dbpass, $dbname);
 *  $this->db->query("INSERT INTO users (name, birthdate) VALUES (?, ?)", array("John Doe", "1970-01-01"));
 *  $id = $this->db->lastInsertId();
 *  $user1 = $this->db->query("SELECT name FROM users WHERE id = ?", $id)->getRow();
 *  $all_users = $this->db->query("SELECT name FROM users")->getResult();
 */
class DB {
	protected $connection;
	protected $query;
	protected $show_errors = true;
	protected $query_closed = true;
	protected $query_count= 0;

	public $error = false;

	public function __construct($dbhost = "localhost", $dbuser = "root", $dbpass = "", $dbname = "", $charset = "utf8") {
		$this->connection = new mysqli($dbhost, $dbuser, $dbpass, $dbname);

		// Check connection
		if ($this->connection->connect_error) {
			$this->error("Database connection failed: " . $this->connection->connect_error);
		}
		$this->connection->set_charset($charset);
	}

	public function __destruct() {
		$this->close();
	}

	public function affectedRows()
	{
		return $this->connection->affected_rows;
	}

	public function close()
	{
		$this->connection->close();
	}

	private function error($error)
	{
		$this->error = $error;

		if ($this->show_errors) {
			exit($error);
		}
	}

	public function getResult() {
		$return = array();
		$mysqli_result = $this->query->get_result();
        if (!$mysqli_result) {
            return false;
        }

		while($row = $mysqli_result->fetch_object()) {
			$return[] = $row;
		}
		return $return;
	}

	public function getRow()
	{
		return $this->query->get_result()->fetch_object();
	}

	private function getType($var)
	{
		if (is_string($var)) { return 's'; }
		if (is_float($var)) { return 'd'; }
		if (is_int($var)) { return 'i'; }
		return 'b';
	}

	public function lastInsertId()
	{
		return $this->connection->insert_id;
	}

	public function numRows()
	{
		$this->query->store_result();
		return $this->query->num_rows;
	}

	public function query($query, ...$args)
	{
		if (!$this->query_closed) {
			$this->query->close();
		}

		if ($this->query = $this->connection->prepare($query)) {
			// Check for arguments
			if (sizeof($args) > 0) {
				// $args can be variable length array or regular array.
				// Check which one it is.
				if (is_array($args[0])) {
					// An array was passed. Move it one level up in the array, so it's the same array as a variable length array
					$args = $args[0];
				}

				$types = "";    // Types of the prepared statements as a string
				$prepared_statement_values = array();
				foreach ($args as $key => &$arg) {
					$types .= $this->getType($args[$key]);
					$prepared_statement_values[] = &$arg;
				}

				// Add the types to the front of the array
				array_unshift($prepared_statement_values, $types);

				// Call the bind_param-function the create the prepared statements
				call_user_func_array(array($this->query, 'bind_param'), $prepared_statement_values);
			}

			// Execute the query
			$this->query->execute();

			// Was there an error?
			if ($this->query->errno) {
				$this->error("Unable to process MySQL query: " . $this->query->error);
			}

			// Close the query and add to the query count
			$this->query_closed = false;
			$this->query_count++;
		} else {
			$this->error("Unable to prepare MySQL statement: " . $this->connection->error);
		}

		return $this;
	}
}