classe per connessione al db

[rocco.mod]

buonasera a tutti , sto cercando di adattare una classe per la connessione al database con mysqli
tutto in un unico files , cerco di spiegere :

definisco le costanti dove inserire i parametri del server tipo host user pass e nome database,

da varifiche si connette al database ma se io vado e scrivo un user errato o nome database errato mi genera un errore il php invece di generasre il comando che voglio io .
posto la classe

Fatal error: Uncaught Error: Call to undefined method DataBase::connect_error()

define("DB_HOST"      ,"localhost");define("DB_USER"      ,"root");define("DB_PASS"      ,"");define("DB_NAME"      ,"test");define("DB_CACHE_TIME",0);define("TABLE_PREFIX" ,"rc_");define("DB_ERROR_MAIL","");define("DB_PORT"      ,"3306");define("PCONNECT"     , false);
if(!empty($db_host)){$db_host = '';}else{$db_host = DB_HOST ;}if(!empty($db_user)){$db_user = '';}else{$db_user = DB_USER ;}if(!empty($db_pass)){$db_pass = '';}else{$db_pass = DB_PASS ;}if(!empty($db_name)){$db_name = '';}else{$db_name = DB_NAME ;}if(!empty($db_cache_time)){$db_cache_time = '';}else{$db_cache_time = DB_CACHE_TIME ;} 

e qua la classe

class DataBase {
public $dbhost            = "";public $dbuser         = "";public $dbpass            = "";public $dbname         = "";public $db_cache_time    = 0;public $connect        = "";public $query            = "";public $dbport            = "";

function DataBase()    {        if(defined("DB_HOST")){$this->dbhost = DB_HOST ; }        if(defined("DB_USER")){$this->dbuser = DB_USER ; }        if(defined("DB_PASS")){$this->dbpass = DB_PASS ; }        if(defined("DB_NAME")){$this->dbname = DB_NAME ; }        if(defined("DB_PORT")){$this->dbport = DB_PORT ; }    } function __construct(){global $db_host ,$db_user ,$db_pass ,$db_name,$db_cache_time ;
$this->dbhost        = $db_host ;$this->dbuser        = $db_user ;$this->dbpass        = $db_pass ;$this->dbname        = $db_name ;$this->db_cache_time = $db_cache_time ;}function  connect(){global $db_host ,$db_user ,$db_pass ,$db_name,$db_cache_time ;
$this->query = new mysqli($this->dbhost ,$this->dbuser ,$this->dbpass ,$this->dbname  )or die($this->connect_error); if( $this->query  == true ){return true ;}else{return false ;} }

function dberror( ){ if ($this->query) {  return $this->connect_error( $this->query ); } return $this->connect_error();}}
$con = new DataBase();
echo '<pre>'; var_dump( $con->connect());  echo '</pre>';echo '<pre>';print_r( $con->dberror());echo '</pre>';