Clean Architecture Clean Architecture in Python in Python - - PowerPoint PPT Presentation

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Clean Architecture Clean Architecture in Python in Python - - PowerPoint PPT Presentation

Feb 28, 2023 139 likes •553 views

Clean Architecture Clean Architecture in Python in Python Sebastian Buczyski Sebastian Buczyski @ PyKonik Tech Talks #36 PyKonik Tech Talks #36 Clean Architecture Clean Architecture 1. Independence of frameworks 2. Testability 3.

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Clean Architecture Clean Architecture

in Python in Python

Sebastian Buczyński Sebastian Buczyński @ PyKonik Tech Talks #36 PyKonik Tech Talks #36

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Clean Architecture Clean Architecture

  • 1. Independence of frameworks
  • 2. Testability
  • 3. Independence of UI
  • 4. Independence of database
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Clean Architecture Clean Architecture Pung customer's concerns in the first place

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Project: Auctions online Project: Auctions online

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User stories User stories

As a bidder I want to make a bid to win an aucon As a bidder I want to be nofied by e‑mail when my offer is a winning one As an administrator I want to be able to withdraw a bid

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Django + Rest Framework! Django + Rest Framework!

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Models first Models first

class Auction(models.Model): title = models.CharField(...) initial_price = models.DecimalField(...) current_price = models.DecimalField(...) class Bid(models.Model): amount = models.DecimalField(...) bidder = models.ForeignKey(...) auction = models.ForeignKey(Auction, on_delete=PROTECT)

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User stories User stories

As a bidder I want to make a bid to win an aucon ✔ As a bidder I want to be nofied by e‑mail when my offer is a winning one ✔ As an administrator I want to be able to withdraw a bid

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def save_related(self, request, form, formsets, *args, **kwargs): ids_of_deleted_bids = self._get_ids_of_deleted_bids(formsets) bids_to_withdraw = Bid.objects.filter( pk__in=ids_of_deleted_bids) auction = form.instance

  • ld_winners = set(auction.winners)

auction.withdraw_bids(bids_to_withdraw) new_winners = set(auction.winners) self._notify_winners(new_winners - old_winners) super().save_related(request, _form, formsets, *args, **kwarg

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def save_related(self, request, form, formsets, *args, **kwargs): ids_of_deleted_bids = self._get_ids_of_deleted_bids(formsets) bids_to_withdraw = Bid.objects.filter( pk__in=ids_of_deleted_bids) auction = form.instance

  • ld_winners = set(auction.winners)

auction.withdraw_bids(bids_to_withdraw) new_winners = set(auction.winners) self._notify_winners(new_winners - old_winners) super().save_related(request, _form, formsets, *args, **kwarg

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def save_related(self, request, form, formsets, *args, **kwargs): ids_of_deleted_bids = self._get_ids_of_deleted_bids(formsets) bids_to_withdraw = Bid.objects.filter( pk__in=ids_of_deleted_bids) auction = form.instance

  • ld_winners = set(auction.winners)

auction.withdraw_bids(bids_to_withdraw) new_winners = set(auction.winners) self._notify_winners(new_winners - old_winners) super().save_related(request, _form, formsets, *args, **kwarg

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Clean Arch - building block #1 Clean Arch - building block #1

UseCase OR Interactor

class WithdrawingBid: def withdraw_bids(self, auction_id, bids_ids): auction = Auction.objects.get(pk=auction_id) bids_to_withdraw = Bid.objects.filter( pk__in=ids_of_deleted_bids)

  • ld_winners = set(auction.winners)

auction.withdraw_bids(bids_to_withdraw) new_winners = set(auction.winners) self._notify_winners(new_winners - old_winners)

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UseCase - Orchestrates a particular process UseCase - Orchestrates a particular process

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What about tests?! What about tests?!

Business logic is coupled with a framework, so are tests...

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Testing through views Testing through views

from django.test import TestCase class LoginTestCase(TestCase): def test_login(self): User.objects.create(...) response = self.client.get('/dashboard/') self.assertRedirects(response, '/accounts/login/')

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How a textbook example looks like? How a textbook example looks like?

No side effects and dependencies makes code easier to test

class MyTest(unittest.TestCase): def test_add(self): expected = 7 actual = add(3, 4) self.assertEqual(actual, expected)

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Getting rid of dependencies: find them Getting rid of dependencies: find them

class WithdrawingBidUseCase: def withdraw_bids(self, auction_id, bids_ids): auction = Auction.objects.get(pk=auction_id) bids_to_withdraw = Bid.objects.filter( pk__in=ids_of_deleted_bids)

  • ld_winners = set(auction.winners)

auction.withdraw_bids(bids_to_withdraw) new_winners = set(auction.winners) self._notify_winners(new_winners - old_winners)

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Getting rid of dependencies: hide them Getting rid of dependencies: hide them

class WithdrawingBidUseCase: def withdraw_bids(self, auction_id, bids_ids): auction = self.auctions_repository.get(auction_id) bids = self.bids_repository.get_by_ids(bids_ids)

  • ld_winners = set(auction.winners)

auction.withdraw_bids(bids) new_winners = set(auction.winners) self.auctions_repository.save(auction) for bid in bids: self.bids_repository.save(bid) self._notify_winners(new_winners - old_winners)

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Getting rid of dependencies: hide them Getting rid of dependencies: hide them

class WithdrawingBidUseCase: def withdraw_bids(self, auction_id, bids_ids): auction = self.auctions_repository.get(auction_id) bids = self.bids_repository.get_by_ids(bids_ids)

  • ld_winners = set(auction.winners)

auction.withdraw_bids(bids) new_winners = set(auction.winners) self.auctions_repository.save(auction) for bid in bids: self.bids_repository.save(bid) self._notify_winners(new_winners - old_winners)

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Clean Arch - building block #2 Clean Arch - building block #2

Interface / Port

class AuctionsRepo(metaclass=ABCMeta): @abstractmethod def get(self, auction_id): pass @abstractmethod def save(self, auction): pass

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Clean Arch - building block #3 Clean Arch - building block #3

Interface Adapter / Port Adapter

class DjangoAuctionsRepo(AuctionsRepo): def get(self, auction_id): return Auction.objects.get(pk=auction_id)

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Combine together Combine together

class WithdrawingBidUseCase: def __init__(self, auctions_repository: AuctionsRepo): self.auctions_repository = auctions_repository django_adapter = DjangoAuctionsRepo() withdrawing_bid_uc = WithdrawingBidUseCase(django_adapter)

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Dependency Injection Dependency Injection

import inject def configure_inject(binder: inject.Binder): binder.bind(AuctionsRepo, DjangoAuctionsRepo()) inject.configure_once(configure_inject) class WithdrawingBidUseCase: auctions_repo: AuctionsRepo = inject.attr(AuctionsRepo)

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Benefits from another layer Benefits from another layer It is easier to reason about logic It is possible to write TRUE unit tests Work can be parallelized Decision making can be delayed

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Our logic is still coupled to a database! Our logic is still coupled to a database!

class WithdrawingBidUseCase: def withdraw_bids(self, auction_id, bids_ids): auction = self.auctions_repository.get(auction_id) bids = self.bids_repository.get_by_ids(bids_ids)

  • ld_winners = set(auction.winners)

auction.withdraw_bids(bids) new_winners = set(auction.winners) self.auctions_repository.save(auction) for bid in bids: self.bids_repository.save(bid) self._notify_winners(new_winners - old_winners)

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Clean Arch - building block #0 Clean Arch - building block #0

Enty

class Auction: def __init__(self, id: int, title: str, bids: List[Bid]): self.id = id self.title = title self.bids = bids def withdraw_bids(self, bids: List[Bid]): ... def make_a_bid(self, bid: Bid): ... @property def winners(self): ...

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Clean Arch - building block #3 Clean Arch - building block #3

Interface Adapter / Port Adapter

class DjangoAuctionsRepo(AuctionsRepo): def get(self, auction_id: int) -> Auction: auction_model = AuctionModel.objects.prefetch_related( 'bids' ).get(pk=auction_id) bids = [ self._bid_from_model(bid_model) for bid_model in auction_model.bids.all() ] return Auction( auction_model.id, auction_model.title, bids )

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All that's left is to call All that's left is to call UseCase from UseCase from Django Django any framework any framework

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Clean Arch building blocks altogether

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What to be careful of? What to be careful of? non‑idiomac framework use more code (type hints help) copying data between objects validaon?

  • verengineering
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When it pays off? When it pays off? lots of cases ‑ testability delaying decision making ‑ stay lean complicated domain

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That's all, folks! That's all, folks!

Questions? Questions?

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Futher reading Futher reading

hps:/ /8thlight.com/blog/uncle‑bob/2012/08/13/the‑clean‑architecture.html Clean Architecture: A Crasman's Guide to Soware Structure and Design Clean Architecture Python (web) apps ‑ Przemek Lewandowski Soware architecture chronicles ‑ blog posts series Boundaries ‑ Gary Bernhardt Exemplary project in PHP (blog post) Exemplary project in PHP (repo) Exemplary project in C# (repo) Exemplary project in Python (repo)

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