ActiveModel.php

<?php

include 'medoo.php';

class ActiveModel {
    public static $table_columns = array();

    public function __construct( $parameters = null ) {
        $class_name = get_class($this);
        $table_name = strtolower($class_name) . 's';

	if( $parameters == null ) {
	    if( count(self::$table_columns) == 0 ) {
	        $database = new medoo();
	        $records = $database->query('SHOW COLUMNS FROM ' . $table_name)->fetchAll();
	
	        foreach ($records as $column_info) {
	            $this->$column_info['Field'] = null;
	            self::$table_columns[] = $column_info['Field'];
	        }	
	    } else {
	        foreach (self::$table_columns as $column_name) {
	            $this->$column_name = null;
	        }	
	    }
	} else {
	    foreach ($parameters as $key => $value) {
                $this->$key = $value;
            }
        }
    }

    public static function find( $ids ) {
        $class_name = get_called_class();
        $table_name = strtolower($class_name) . 's';

        $database = new medoo();
        $records = $database->select( $table_name, "*", [ 'id[=]' => $ids ] );
	
        $objs = [];
        foreach ($records as $record) {
	    $o = new $class_name();
	    foreach ($record as $key => $value) 
                $o->$key = $value;
    
            if( $o->belongs_to !== null ) {
                $belongsRecord = $database->select( $o->belongs_to . 's',  "*", [ 'id[=]' => $o->{$o->belongs_to . '_id'} ]);
                $belongs_to_class = ucfirst( $o->belongs_to );

                $o->{$o->belongs_to} = new $belongs_to_class($belongsRecord[0]);
            }

            if( $o->has_many !== null ) {
                $hasManyRecord = $database->select( $o->has_many, "*", [ strtolower($class_name) . '_id[=]' => $o->id] );
                $hasManyClass = substr(ucfirst($o->has_many), 0, -1);
                $o->{$o->has_many} = array();
               
                foreach ($hasManyRecord as $record) 
                    $o->{$o->has_many}[] = new $hasManyClass($record);			
            }

            $objs[] = $o;
        }

        return $objs;
    }

    public function __get($name) {
        if ( isset( $this->$name ) )
            return $this->$name;
                return null;
    }
}

/*

Tables in DB

    Table `users`
 	id => primary_key int(11) unsigned A_I
	name => varchar(45)
	pwd => varchar(45)

   Table `posts`
	id => primary_key int(11) unsigned A_I
	body => varchar(45)
	user_id => index int(11) unsigned constraints{ondelete: cascade, onupdate: noaction}

*/

class Post extends ActiveModel {
    public $belongs_to = 'user';
}

class User extends ActiveModel {
    public $has_many = 'posts';
}