I'm using [php activerecord](http://phpactiverecord.org/). I need initialize a `Order` object and then set related objects as show below

```
$order = new Order();
Order->_plan = Plan::find(1);

```

I get the error `Undefined property: Order->_plan in /var/www/ordenes-web/core/libs/php-activerecord/lib/Model.php on line 428`

My class:

```
class Order extends ActiveRecord\Model{
    static $belongs_to = array( 
        array(
            '_plan',
            'class_name' => 'Plan',
            'foreign_key' => 'plan'
        ),
    );
}

```

The relationship works fine. If I find an `Order` with the finder I get the related object `_plan`:

```
Order::find(1)->_plan // Works!

```

What am I doing wrong?