<?php

class User extends ActiveRecord {
    public $id;
    public $email;
    public $password;
    public $firstName;
    public $lastName;
}

/* maps all this on table:

Table users
------------------------
| id          | int    |
| email       | string |
| password    | string |
| first_name  | string |
| last_name   | string |
------------------------ */

abstract class ActiveRecord {
    public function save() {
        if ($this->isNewRecord()) {
            $this->insert();
        } else {
            $this->update();
        }
    }
    public function update() {
        $this->db->update($this->tableName, $this->attrs, ['id' => $this->id]);
    }
    
    public function insert() {
        $this->db->insert($this->tableName, $this->attrs);
    }
    
    public function delete() {
        $this->db->insert($this->tableName, $this->attrs);
    }
    // ...
}