Django dalle trincee: pattern e pratiche dopo 15 anni di esperienza su Django

In 15 anni di esperienza, ne ho viste, di cose, che voi umani ...
Nonostante Django fornisca un'architettura di base molto pulita e linee guida per aiutare una buona organizzazione del progetto, le cose possono sfuggire di mano e portare rapidamente il progetto ad essere un piatto di spaghetti in salsa pythonica.

La ricetta perfetta non esiste, perché ogni progetto di una certa complessità ha le sue particolarità e le sue caratteristiche che richiedono un approccio individuale.

Un buon progetto parte però dal processo di sviluppo, si parte quindi con alcune riflessioni sulle pratiche che nel tempo sono state efficaci negli migliorare la qualità dello sviluppo.

Successivamente, saranno presentati alcuni pattern, dettati da un approccio pragmatico e basato sull'esperienza, che possano essere un'ispirazione per i propri progetti.

I principi che ispirano questi pattern sono di favorire l'estendibilità del codice e la manutenibilità, e per migliorare la comunicazione e la documentazione del progetto per gestire in modo più efficiente il ciclo di vita del progetto stesso

Transcript

1. Django dalle Trincee Consigli e pattern da 15 anni di django Iacopo Spalletti @ Nephila PyConIT 2025 30 May 2025 Iacopo Spalletti - @yakkys
2. Iacopo Spalletti - @yakkys
3. Iacopo Spalletti - @yakkys
4. Iacopo Spalletti - @yakkys
5. Iacopo Spalletti - @yakkys
6. Problemi! Problemi! Problemi! Iacopo Spalletti - @yakkys
7. Issues and Symptoms messy code fragile architecture challenging maintenance high costs of adding features complex deploys Iacopo Spalletti - @yakkys
8. Iacopo Spalletti - @yakkys
9. Why? Every person is different Unique combination of strengths and weaknesses No silver bullet Iacopo Spalletti - @yakkys
10. Why? Every team is different Unique combination of people and conditions No silver bullet Iacopo Spalletti - @yakkys
11. Why? Every project is different Unique combination of constraints and challenges No silver bullet Iacopo Spalletti - @yakkys
12. Iacopo Spalletti - @yakkys
13. Iacopo Spalletti - @yakkys
14. What if I work alone? In team with your future self Iacopo Spalletti - @yakkys
15. Best intentions → Best practices Iacopo Spalletti - @yakkys
16. Which? Iacopo Spalletti - @yakkys
17. Code Review Iacopo Spalletti - @yakkys
18. In a team communication introducing new approaches improve team skills grow junion members Code Review Iacopo Spalletti - @yakkys
19. Caveats Working Agreements Respectful communication Code Review Iacopo Spalletti - @yakkys
20. Flying solo Code Review Iacopo Spalletti - @yakkys
21. The gateway zero tooling enabler for further steps Code Review Iacopo Spalletti - @yakkys
22. Linting / formatting black / isort ruff pre-commit Next steps Iacopo Spalletti - @yakkys
23. Documentation docstrings architecture schemes and diagrams Next steps Iacopo Spalletti - @yakkys
24. Sphinx Easy to integrate in the same repository Enable autodoc features to extract information from code Static rendering Documentation 1 # 2 import os 3 import sys 4 sys.path.insert(0, os.path.absp 5 project = 'My Project' 6 copyright = 'Myself' 7 author = 'myself' 8 extensions = ['sphinx.ext.autod 9 templates_path = ['_templates'] 10 exclude_patterns = ['_build'] 11 #html_static_path = ['_static'] 1 Architecture 2 ============== 3 .... 4 5 Models 6 =========== 7 8 .. automodule:: my_project.my_a 9 :members: Iacopo Spalletti - @yakkys
25. Tests Next steps Iacopo Spalletti - @yakkys
26. Being in Control Client doesn’t pay for tests The boss thinks they’re a waste Do I really need tests? It’s obvious that this code works Tests Iacopo Spalletti - @yakkys
27. You don’t have to be perfect You don’t need TDD You don’t need 100% coverage Something is better than nothing Tests Iacopo Spalletti - @yakkys
28. Automate, Automate, Automate Iacopo Spalletti - @yakkys
29. Until it’s too much Iacopo Spalletti - @yakkys
30. What to automate? Whatever can change in a commit Code style Tests Security checks dependencies: pip-audit static code analysis: bandit Builds Deployments Iacopo Spalletti - @yakkys
31. CI Plenty of hosted options (Github Actions, …) Self-hosted platforms available (Gitlab, …) Iacopo Spalletti - @yakkys
32. Beyond CI Yeah, CI is cool, but have you tried automating commands? bash Just Fabric Ansible Terraform / OpenTofu Iacopo Spalletti - @yakkys
33. Deployment Example 1 @task 2 def deploy(connection): 3 if not connection.run(f"test -d {repo_dir}", warn=True).ok: 4 commands.append(f"git clone {repo_url} {repo_root}") 5 else: 6 commands.append(f"cd {repo_root} && git fetch") 7 connection.run(f"cd {repo_root} && git checkout origin/{branch}") 8 connection.run(f"cd {repo_root} && python{python} -m venv {VIRTUALENV}") 9 connection.run(f"cd {repo_root} && {VIRTUALENV}/bin/python -m pip install -r requirements_live.txt") 10 connection.run(f"cd {repo_root} &&" f"{VIRTUALENV}/bin/python manage.py migrate --noinput") 11 connection.run(f"cd {repo_root} &&" f"{VIRTUALENV}/bin/python manage.py collectstatic -c --noinput") Iacopo Spalletti - @yakkys
34. Observability Iacopo Spalletti - @yakkys
35. Sentry Jaeger Observability Iacopo Spalletti - @yakkys
36. "Observing Python applications with OpenTelemetry" by Riccardo Magliocchetti Observability Iacopo Spalletti - @yakkys
37. Iterate, Iterate, Iterate gain confidence gain velocity to invest in new practices gain reliability Iacopo Spalletti - @yakkys
38. Iacopo Spalletti - @yakkys
39. Iacopo Spalletti - @yakkys
40. Iacopo Spalletti - @yakkys
41. Prime principles SOLID Patterns Architectural Patterns Clean code DDD … Iacopo Spalletti - @yakkys
42. Be pragmatic Iacopo Spalletti - @yakkys
43. Embrace idiomatic Django Generic views are your friends Fat Model, Skinny View Fat Model, Chubby Querysets Be pragmatic Iacopo Spalletti - @yakkys
44. Caveat Sample code, don’t try this (verbatim) at home Iacopo Spalletti - @yakkys
45. Generic views are your friends Embrace idiomatic Django 1 class TransferFundView(UpdateView): 2 model = BankAccount 3 fields = ["amount"] 4 5 class BankAccount(models.Model): 6 amount = models.DecimalField(decimal_places=2, max_digits=10) Iacopo Spalletti - @yakkys
46. Generic views are your friends Embrace idiomatic Django 1 class TransferFundView(UpdateView): 2 model = BankAccount 3 form_class = TransferFundForm 4 5 class TransferFundForm: 6 class Meta: 7 model = BankAccount 8 fields = ["amount"] 9 10 def clean_amount(self): 11 if self.cleaned_data["amount"] < 0: 12 raise ValidationError("Amount must be positive") 13 return self.cleaned_data["amount"] 14 15 class BankAccount(models.Model): 16 amount = models.DecimalField(decimal_places=2, max_digits=10) Iacopo Spalletti - @yakkys
47. Fat Model, Skinny View Embrace idiomatic Django 6 def save(self, *args, **kwargs): 7 return self.instance.transfer_amount(self.cleaned_data["amount"]) 12 def transfer_amount(self, new_amount): 13 self.amount = new_amount 14 self.save() 15 return self 1 class TransferFundForm: 2 class Meta: 3 model = BankAccount 4 fields = ["amount"] 5 8 9 class BankAccount(models.Model): 10 amount = models.DecimalField(decimal_places=2, max_digits=10) 11 Iacopo Spalletti - @yakkys
48. Fat Model, Skinny View Permissions Object filtering Template rendering Form processing Embrace idiomatic Django 1 class TransferFundView(UpdateView): 2 model = BankAccount 3 form_class = TransferFundForm 4 5 ??? Iacopo Spalletti - @yakkys
49. Fat Model, Chubby QuerySet Embrace idiomatic Django 1 class BankAccountQuerySet(models.QuerySet): 2 3 def green_accounts(self): 4 return self.filter(amount__gt=0) 5 6 class BankAccount(models.Model): 7 amount = models.DecimalField(decimal_places=2, max_digits=10) 8 9 objects = BankAccountQuerySet.as_manager() 10 11 rich_accounts = BankAccount.objects.green_account() Iacopo Spalletti - @yakkys
50. Bonus hint django-filter django-model-utils Embrace idiomatic Django Iacopo Spalletti - @yakkys
51. Separating the business logic Iacopo Spalletti - @yakkys
52. Service / Use Case Links: DDD Clean Architecture … Iacopo Spalletti - @yakkys
53. Example Service 1 class HandleTransferFunds: 2 @staticmethod 3 def deposit(source_account, target_account, amount): 4 with atomic(): 5 if source_account.has_available(amount): 6 source_account.remove(amount) 7 target_account.add(amount) 8 9 HandleTransferFunds.deposit(account_1, account_2, 100) Iacopo Spalletti - @yakkys
54. Composition >> Inheritance django is all about inheritance but your logic doesn’t have to Service Iacopo Spalletti - @yakkys
55. Stateless? Service 1 @dataclass 2 class HandleTransferFunds: 3 source: Account 4 target: Account 5 amount: Decimal 6 7 def run(self): 8 with atomic(): 9 if self.source.has_available(self.amount): 10 self.source.remove(self.amount) 11 self.target.add(self.amount) 12 13 HandleTransferFunds(account_1, account_2, 100).run() Iacopo Spalletti - @yakkys
56. Oops Service 1 def handle_transfer_funds(source_account, target_account, amount): 2 with atomic(): 3 if source_account.has_available(amount): 4 source_account.remove(amount) 5 target_account.add(amount) Iacopo Spalletti - @yakkys
57. A more realistc example Service 1 @dataclass 2 class TransferVideo: 3 source_account: str 4 target_account: str 5 video_source_class: AbstractVideoService 6 video_target_class: AbstractVideoService 7 8 def _get_video_client(self, video_class, account): 9 instance = video_class(account) 10 return instance 11 12 def _transfer(self, source, target): 13 source_video = source_client.get_video() 14 target_client.upload_video(source_video) 15 16 def run(self): 17 source_client = self._get_video_client(self.video_source_class, self.source_account) 18 target_client = self._get_video_client(self.video_target_class, self.target_account) 19 self._transfer(source_client, target_client) Iacopo Spalletti - @yakkys
58. What about Django? Service Iacopo Spalletti - @yakkys
59. Iacopo Spalletti - @yakkys
60. Django sequence Logic Model Form View Logic Model Form View Instantiate Instantiate Validate Errors Save Execute Execute Execute Errors Iacopo Spalletti - @yakkys
61. Service sequence Model Service Form View Model Service Form View Instantiate Instantiate Validate Errors Instantiate Execute Save Errors Errors Iacopo Spalletti - @yakkys
62. Django sequence Adding logic 13 def handle_transfer_funds(source_account, target_account, amount): 14 with atomic(): 15 if source_account.has_available(amount): 16 source_account.remove(amount) 17 target_account.add(amount) 1 class TransferFundView(UpdateView): 2 model = BankAccount 3 form_class = TransferFundForm 4 5 class TransferFundForm: 6 class Meta: 7 model = BankAccount 8 fields = ["amount"] 9 10 class BankAccount(models.Model): 11 amount = models.DecimalField(decimal_places=2, max_digits=10) 12 Iacopo Spalletti - @yakkys
63. View hard to reuse hard to test logic scattered across the codebase 🤨 Adding logic 1 class TransferFundView(UpdateVi 2 model = BankAccount 3 form_class = TransferFundFo 4 5 def form_valid(self, form): 6 ... 7 with atomic(): 8 if source_account.h 9 source_account. 10 target_account. 11 return super().form_val Iacopo Spalletti - @yakkys
64. Form less hard to reuse less hard to test logic scattered across the codebase 😐 Adding logic 1 class TransferFundForm(models.M 2 3 class Meta: 4 model = BankAccount 5 fields = ["amount"] 6 7 def __init__(self, target, 8 self.target = target 9 ... 10 11 def save(self, *args, **kwa 12 with atomic(): 13 if instance.has_ava 14 instance.remove 15 self.target.add 16 return instance Iacopo Spalletti - @yakkys
65. ⚠️ Try this at home carefully Adding logic Iacopo Spalletti - @yakkys
66. Service Adding logic 1 @dataclass 2 class HandleTransferFunds: 3 source: Account 4 target: Account 5 amount: Decimal 6 7 def run(self): 8 with atomic(): 9 if self.source.has_available(self.amount): 10 self.source.remove(self.amount) 11 self.target.add(self.amount) Iacopo Spalletti - @yakkys
67. Service Adding logic 1 @dataclass 2 class HandleTransferFunds: 3 source: Account 4 target: Account 5 amount: Decimal 6 7 def validate(): 8 if not self.source.has_available(self.amount): 9 raise ValidationError("Not enough funcs") 10 return True 11 12 def run(self): 13 with atomic(): 14 if self.validate(): 15 self.source.remove(self.amount) 16 self.target.add(self.amount) Iacopo Spalletti - @yakkys
68. Form Adding logic 11 def save(self, commit=True): 12 try: 13 instance = self.logic.run() 14 except ValidationError as e: 15 self.add_error(None, e) 16 raise 1 class TransferFundForm(models.ModelForm): 2 3 class Meta: 4 model = BankAccount 5 fields = ["amount"] 6 7 def clean(): 8 self.logic.validate() 9 ... 10 17 return instance Iacopo Spalletti - @yakkys
69. View Adding logic 5 def form_valid(self, form): 6 try: 7 return super().form_valid(form) 8 except (ValueError, ValidationError) as e: 9 return super().form_invalid(form) 1 class TransferFundView(UpdateView) 2 model = BankAccount 3 form = TransferFundForm 4 Iacopo Spalletti - @yakkys
70. Wrap-up Is it worth? It depends 😄 Adding logic Iacopo Spalletti - @yakkys
71. Tradeoffs Reuse 👍 Test 👍 Isolation 👍 Complexity 👎 Non idiomatic code 👎 Adding logic Iacopo Spalletti - @yakkys
72. Asynchronous communication Iacopo Spalletti - @yakkys
73. Pub-sub Asynchronous communication Iacopo Spalletti - @yakkys
74. Case Listen on a webhook and run some logic on a mixed set of web applications Pub-sub Iacopo Spalletti - @yakkys
75. Publisher Pub-sub 17 request.app.state.redis_client.publish("order", json.dumps(message)) 1 def get_publisher(app): 2 app.state.redis_client = redis.Redis.from_url(url=url) 3 yield 4 5 app = FastAPI(lifespan=get_publisher) 6 7 @app.api_router("/send_message/{msg_type}/{order}/{status}/") 8 async def send_message(request, msg_type: str, order: int, status: str): 9 message = { 10 "type": msg_type, 11 "message": { 12 "order": order, 13 "date": now().isoformat("%c"), 14 "status": status, 15 }, 16 } 18 return Response("ok") Iacopo Spalletti - @yakkys
76. Subscriber How to subscribe in django? Pub-sub Iacopo Spalletti - @yakkys
77. Subscriber - Channels version Pub-sub 12 while await channel.wait_message(): 13 msg = await channel.get_json() 14 await MessageStatusDispatcher(self, msg).execute() 1 class OrderStatusConsumer(AsyncJsonWebsocketConsumer): 2 3 async def connect(self): 4 await self._subscribe() 5 6 async def _subscribe(): 7 redis = await aioredis.create_redis(settings.REDIS_URL) 8 subscriber_object = await redis.subscribe("order") 9 self._read_messages(subscriber_object[0]) 10 11 async def _read_messages(msg, channel): Iacopo Spalletti - @yakkys
78. Subscriber - Celery version Pub-sub 10 for message in pubsub.listen(): 11 message_handler(message) 1 @worker_ready.connect 2 def at_start(sender, **kwargs): 3 start_redis_subscriber_task.delay() 4 5 @shared_task 6 def start_redis_subscriber_task(): 7 redis_client = redis.Redis.from_url(url=settings.REDIS_URL) 8 pubsub = redis_client.pubsub() 9 pubsub.subscribe("order") Iacopo Spalletti - @yakkys
79. Handling messages Pub-sub 1 HANDLERS = { 2 "paid": PaidOrder, 3 "shipped": ShippedOrder, 4 ... 5 } 6 7 def message_handler(message): 8 handler_class = HANDLERS[message["type"]] 9 handler_class(message).run() Iacopo Spalletti - @yakkys
80. Strengths Full decoupling publisher / subscriber Mixed technologies Different use cases Webhooks IoT … Pub-sub Iacopo Spalletti - @yakkys
81. Iacopo Spalletti - @yakkys
82. Iacopo Spalletti Founder and CTO @Nephila_digital Djangonaut and open source developer @yakky@mastodon.social https://github.com/yakky https://speakerdeck.com/yakky Iacopo Spalletti - @yakkys
83. Questions? Iacopo Spalletti - @yakkys
84. Thanks! Iacopo Spalletti - @yakkys
85. Linkography / 1 Team Tuckman’s stages of group development Automation tools bash Just Fabric Ansible Terraform OpenTofu Iacopo Spalletti - @yakkys
86. Linkography / 2 Useful packages django-filter django-model-utils DDD Implementing Domain-Driven Design in Django Decoding DDD: A Three-Tiered Approach to Django Projects Against service layer Iacopo Spalletti - @yakkys