I was trying to find examples for using DDD factories and I came across the shipping application from Eric Evans’ book.
However when I checked the BookingService the code to create a Cargo had this comment at line 37:
34 public TrackingId bookNewCargo(final UnLocode originUnLocode,
35 final UnLocode destinationUnLocode,
36 final Date arrivalDeadline) {
37 // TODO modeling this as a cargo factory might be suitable
38 final TrackingId trackingId = cargoRepository.nextTrackingId();
39 final Location origin = locationRepository.find(originUnLocode);
40 final Location destination = locationRepository.find(destinationUnLocode);
41 final RouteSpecification routeSpecification = new RouteSpecification(origin, destination, arrivalDeadline);
42
43 final Cargo cargo = new Cargo(trackingId, routeSpecification);
44
45 cargoRepository.store(cargo);
46 logger.info("Booked new cargo with tracking id " + cargo.trackingId().idString());
47
48 return cargo.trackingId();
49 }
How should the DDD factory be used here? Which parts exactly should be refactored to use the factory in these piece of code?
Lines 38 to 43 could be classed as domain logic as this is how you create a valid cargo. Given that the booking service is an application service it should be delegating to the domain layer to create a cargo. Maybe the code would look like so…
37 // TODO modeling this as a cargo factory might be suitable
38 final TrackingId trackingId = cargoRepository.nextTrackingId();
39 final Location origin = locationRepository.find(originUnLocode);
40 final Location destination = locationRepository.find(destinationUnLocode);
42
43 final Cargo cargo = CargoFactory.create(trackingId, origin, destination);
Check out my free book on DDD https://leanpub.com/Practicing-DDD for more info on factory implementations.