รบกวนช่วยเหลือกับการเขียนคลาสของ mysqli ไว้ใช้งานด้วยครับ

<?php
class MyDB {
	
	function __construct()
	{
		$this->connection = new mysqli(DBHOST, DBUSER, DBPASS, DBNAME) or die('ไม่สามารถติดต่อฐานข้อมูลได้');
		$this->connection->set_charset('utf8');
	}
	
	
	private function getTypes($item)
	{
		switch (gettype($item))
		{
            case 'NULL':
            case 'string':
                return 's';
                break;

            case 'integer':
                return 'i';
                break;

            case 'blob':
                return 'b';
                break;

            case 'double':
                return 'd';
                break;
		}
		
	}
	
	public function insert($table, $data = array())
	{
		
		$fields = array();
		$values = array();
		$valiable_types = array();
		$values_prepare = array();

		foreach ($data as $field => $value)
		{
			$fields[] = $field;
			$values[] = "'" . $value . "'";
			$valiable_types[] = $this->getTypes($value);
			$values_prepare[] = '?';
		
		}
		
		$field = implode(', ', $fields);
		$value = implode(', ', $values);
		$valiable_type = implode('', $valiable_types);
		$value_prepare = implode(', ', $values_prepare);
		
		
		$stmt = $this->connection->prepare("INSERT INTO $table ($fields) VALUES ($value_prepare)");
		$stmt->bind_param("$valiable_type", $value);
		$stmt->execute();
?>