I am learning some OOP on PHP and I have developed some sample code to practise.

Ignoring the functionality, I just want to learn the "best" or "better" way to write OOP codes in PHP.

The following is my code and I hope anyone who has been doing PHP can help to review or comment for any improvements or weaknesses on my code.

I want to develop my style of code in which copy-and paste is minimum and functionality expandability is rich. For example, the execute() function in the UserDB class is basically the same function and can be used widespread in many diff db class. Do I need to copy and paste the code again or should I just moved this piece of code to abstract class?

How can I optimized my code to made it better for future functionalities such as other select, insert, update and delete while maintaining readability and still within OOP standards?

<?php

    require_once "sys_config.php";
    require_once "general.inc";
    $para[":user"]= "%";

    $dataset = UserFactory::getUsers($para);

    var_dump($dataset);

?>

UserFactory class

<?php

    class UserFactory{

        public static function getUsers($para)
        {
            $db = new UserDB("CALL getUsers(:user)",$para); //sp

            $objs = $db->execute();
            if(!empty($objs))
                foreach( $objs as $obj)
                {
                    $users[] = new user($obj);
                }
            return $users;
        }
                
    }


?>

UserDB class

<?php

    Class UserDB extends Database{

        protected $conn;
        protected $SQL;
        protected $para;

        function __construct($SQL, $para)
        {
            parent::__construct();
                    
            $this->conn = parent::getConn();
            $this->SQL = $SQL;
            $this->para = $para;
        }

        function execute()
        {
                    
            $query = $this->conn->prepare($this->SQL);
            if(!empty($this->para))
                foreach($this->para as $key=>$val)
                {
                    $query->bindParam($key,$val);
                }
            $results = $query->execute();
                    
            $dataset = null;
                    
            if($results)
            {
                while($row = $query->fetch(PDO::FETCH_OBJ))
                {
                    $dataset[]=$row;
                }
            }   
                
            unset($this->conn); 
                    
            parent::__destruct();
                    
            return $dataset;

        }
                
    }

?>

Database abstract class

<?php

    abstract Class Database{

        protected $conn;
                
        function __construct()
        {
            $this->conn = new PDO ("mysql:host=".DB_LOCATION.";dbname=".DB_NAME,DB_USER,DB_PASS);
                
        }
                
        function __destruct()
        {
            unset($this->conn);
                
        }

        function getConn()
        {
            return $this->conn;
        }

        abstract function execute();
    }

?>

User object class

<?php

    class User{

        private $fullname;
        private $id;
                
        function __construct($userObj)
        {
            $this->fullname = $userObj->fullName;
            $this->id = $userObj->id;
        }
                
        function setFullname($fullname)
        {
            $this->fullname = $fullname;
        }
                
        function getFullname()
        {
            return $this->fullname;
        }
                
        function setId($id)
        {
            $this->id = $id;
        }
                
        function getId()
        {
            return $this->id;
        }
    }

?>