Hexagonal Design in Django

  • 324 views
Uploaded on

Flash talk given on 7 aug 2013 for the Amsterdam Python Meetup Group

Flash talk given on 7 aug 2013 for the Amsterdam Python Meetup Group

More in: Technology , Business
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
    Be the first to like this
No Downloads

Views

Total Views
324
On Slideshare
0
From Embeds
0
Number of Embeds
0

Actions

Shares
Downloads
5
Comments
0
Likes
0

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide

Transcript

  • 1. Hexagonal Design in Django Maarten van Schaik
  • 2. Django • Rapid application development • ./manage.py startapp polls • Define some models, forms, views and we’re in business!
  • 3. Applications live and grow • More features are added: – API access – Reporting – Command Line Interface – Integration with other applications – Who knows what else…
  • 4. Connected Design • Components can access all other components • When you need to access a piece of data or a piece of logic, just import and use it • Development is fast
  • 5. Modular design • Access to other components goes through well-defined interfaces (API’s) using well- defined protocols • Components have high cohesion • Components are loosely coupled
  • 6. Connected vs Modular
  • 7. Ports and Adapters
  • 8. Ports and Adapters • Specific adapter for each use of the application, e.g. web view, command line, message queue, etc. • Each adapter connects to a port of the application • Mock adapters and test harnesses facilitate testing • Testing becomes easier and faster
  • 9. Typical Django app • __init__.py • admin.py • forms.py • models.py • tests.py • urls.py • views.py
  • 10. App Uh oh… • Where is my application? ?? Models Views Forms
  • 11. Refactoring Django apps • Rules – Core domain model cannot depend on Django – Tell objects, ask values
  • 12. Implications • Core model cannot depend on framework – Core model cannot derive from models.Model – Communication with Django goes through adapters • Tell, don’t ask – Views should render from immutable values – So no vote.save() in views.py!
  • 13. Example – Poll def vote(request, poll_id): p = get_object_or_404(Poll, pk=poll_id) try: selected_choice = p.choice_set.get( pk=request.POST*‘choice’+) except (KeyError, Choice.DoesNotExist): return render(request, …, ,error: …-) else: selected_choice.votes += 1 selected_choice.save() return HttpResponseRedirect(…)
  • 14. Example – Poll def vote(request, poll_id): p = get_object_or_404(Poll, pk=poll_id) try: selected_choice = p.choice_set.get( pk=request.POST*‘choice’+) except (KeyError, Choice.DoesNotExist): return render(request, …, ,error: …-) else: selected_choice.votes += 1 selected_choice.save() return HttpResponseRedirect(…) Mutating data!
  • 15. Example – Poll (2) def vote(request, poll_id): try: poll_engine.register_vote(poll_id, request.POST*‘choice’+) except Exception as e: return render(request, …, ,error: …-) else: return HttpResponseRedirect(…)
  • 16. Example – Poll (2) ## Poll engine def register_vote(poll_id, choice_id): p = Poll.objects.get(pk=poll_id) selected_choice = p.choice_set.get(pk=choice_id) selected_choice.votes += 1 selected_choice.save()
  • 17. Example – Poll (2) ## Poll engine def register_vote(poll_id, choice_id): p = Poll.objects.get(pk=poll_id) selected_choice = p.choice_set.get(pk=choice_id) selected_choice.votes += 1 selected_choice.save() Dependency on Django models
  • 18. Example – Poll (3) ## Poll engine def register_vote(poll_id, choice_id): if not poll_repository.choice_exists(poll_id, choice_id): raise PollException(…) poll_repository.increment_vote_count(choice_id)
  • 19. Example – Poll (3) ## Django model adapter def choice_exists(poll_id, choice_id): return Choice.objects.filter( poll_id=poll_id, pk=choice_id).exists() def increment_vote_count(choice_id) Choice.objects.filter(pk=choice_id).update( votes=F(‘votes’)+1)
  • 20. Conclusions • Hexagonal design will help keep speed of adding new features constant • Encourages modularity and encapsulation • Encourages clean and well-organized applications • Tests become faster when using plain objects and data • Django models are not that useful without coupling with them
  • 21. That’s it
  • 22. Thanks and references • Matt Wynne: Hexagonal Rails • Kent Beck: To Design or Not To Design? • Alistair Cockburn: Hexagonal Architecture • Django tutorial