Phalcon ORM field has relation with another field in same table

I have the following table in my mysql DB

I have a model Shipment and i am using Phalcon's ORM to interact with my DB. The master_id field in this table is actually the id of another raw, but in the same table, as you can see in the picture. The id=1 is the Master Shipment and id=2 and id=3 are Subshipments.

My model right now looks like this

class Shipment extends Model
{
    protected $id;
    protected $hawb;
    protected $master_id;

    public function initialize()
    {
        parent::initialize();

        $this->hasMany(
            'id',
            'Shipment',
            'master_id'
        );
    }
    //setters and getters are here
}

When I am using $shipment = ShipmentModel::findFirst($id); in my Controller, i can see the master_id of the Shipment.

What i want to have is, call another function from my Shipment model in order to retrieve all the SubShipments as a Collection of Shipment models, or at least an array with Shipment models.

Or even better, if the ShipmentModel::findFirst($id); could populate the SubShipments automatically (if there are any) would be the best!

I don't really know if the $this->hasMany that I have is correct over there, so if someone could show me how to proceed I would be grateful :)

You need to provide full namespace, not just class name - to solve this Model 'Shipment' could not be loaded. Best is to add alias:

$this->hasMany(
    'id',
    Shipment::class,
    'master_id',
    ['alias' => 'subShipments'])
);

And then just use:

Shipment::findFirst()->getSubShipments() you can add such method if you want and do return $this->getRelated('subShipments')