OOP

<?php
defined("BASEPATH") or die("Access Denied");
/**
 * Database
 */
class DB
{
   public $connect;
   public $host;
   public $user;
   public $pass;
   public $database;
   public function __construct()
   {
      $this->host = "localhost";
      $this->user ="root";
      $this->pass = "";
      $this->database = "lks";
      $this->connect = mysqli_connect($this->host,$this->user,$this->pass,$this->database) or die(mysqli_errno());
   }
   public function query($data){
      return mysqli_query($this->connect,$data) or die(mysqli_error($connect));
   }
   public function select($table,$num=null){
      $query = "SELECT * FROM ".$table;
      if($num){
         return $this->num($query);
      }
      return $this->fetch($query);
   }
   public function insert($data,$table){
      $query = "INSERT INTO ";
      if(is_array($data)){
         $value = "'".implode("','",$data)."'";
         $key = "'".implode("','",array_keys($data))."'";
         $query .= "(".$key.") VALUES (".$key.")";
      }
      else {
         $query = "VALUES(".$data.")";
      }
      $query .= " FROM ".$table;
      return $this->query($query);
   }
   public function delete($table,$where){
      $query = "DELETE FROM ".$table." WHERE ";
      if(is_array($where)){
         $i = 0;
         foreach ($where as $key=>$value) {
            $query .= "'".$key."'='".$value."'";
            if(count($where)-1 != $i){
               $query .= ",";
            }
            $i++;
         }
      }
      else {
         $query .= $where;
      }
      return $this->query($query);
   }
   public function update($data,$table,$where){
      $query = "UPDATE ".$table." SET ";
      if(is_array($data)){
         $i = 0;
         foreach ($data as $key=>$value) {
            $query .= "'".$key."'='".$value."'";
            if(count($data)-1 != $i){
               $query .= ",";
            }
            $i++;
         }
      }
      else {
         $query .= $data;
      }
      $query .= " WHERE ";
      if(is_array($where)){
         $i = 0;
         foreach ($where as $key=>$value) {
            $query .= "'".$key."'='".$value."'";
            if(count($where)-1 != $i){
               $query .= ",";
            }
            $i++;
         }
      }
      else {
         $query .= $where;
      }
      return $this->query($query);
   }
   public function fetch($data,$type=null,$type2=MYSQLI_BOTH){
      $data = mysqli_query($this->connect,$data) or die(mysqli_error($connect));
      if($type != null){
         return mysqli_fetch_array($data,$type2);
      }
      else {
         return mysqli_fetch_object($data);
      }
   }
   public function num($data){
      $data = mysqli_query($this->connect,$data) or die(mysqli_error($connect));
      return mysqli_num_rows($data);
   }
}
$db = new DB;
$data = [
   "id_user"=>'',
   "username" =>"ppabcd",
   "password" =>md5("q1w2e3r4t5"),
   "nama" =>"Reza Juliandri",
   "email" =>"asdasd",
   "token" =>"asdasd",
   "creation_date" =>"asdasd",
   "last_login" =>"asdasd"
];
$result = $db->insert($data,"user");
var_dump($result);