SA relationship updates

example.py

class ScannedPort:
    label: str = ""

clsas ScannedDevice:
    hostname: str = ""
    ports: List[ScannedPort] = []

class Port(Base):
    hostname = Column(String, ForeignKey("Device.hostname")
    label = Column(String)
    
class Device(Base):
    hostname = Column(String, primary_key=True)
    ports = relationship(Port)

def existing_or_new(...): ...
    """
    See https://stackoverflow.com/a/52911047
    """
    
def process(session: Session, from_network: ScannedDevice) -> Device:
    device = existing_or_new(Device, hostname=from_network.hostname)
    device.ports = []  # not actual code, but representative of the existing logic
    for port in from_network.ports:
        tmp = existing_or_new(Port, hostname=from_network.hostname, label=from_network.label)
        device.ports.append(tmp)
    return device