Is there a way to simplify this Django query?

Question

accepted_bids = Bid.objects.filter(shipment__user=u, status='acc').select_related('shipment')
completed_shipments = []
for b in accepted_bids:
    completed_shipments.append(b.shipment)
vehicles_shipped = []
for s in completed_shipments:
    vehicles_shipped.extend(s.items.all())

In the end, I want a list of shipped vehicles. A vehicle is shipped if it's part of a shipment that's completed. A shipment is completed if it has an accepted bid.

I'd prefer not to iterate over the querysets thereby forcing a hit to the DB before its necessary... isn't there a way to get all the associated shipments from a list of bids, for example?

---

Here's the trimmed down version of my models:

class Shipment(Model):
    user = ForeignKey(User, related_name='shipments')

class ShipmentItem(models.Model):
    shipment = ForeignKey(Shipment, related_name='items')

    class Meta:
    abstract = True

class VehicleItem(ShipmentItem):
    pass

class Bid(Model):
    user = ForeignKey(User, related_name='bids')
    shipment = ForeignKey(Shipment, related_name='bids')

Answer 1

Supplying the schema is important. But here's a guess:

Vehicle.objects.filter(shipment__bid__status='acc', shipment__user=u)