django-patterns

Name: django-patterns
Author: tranhieutt

69stars41forks

How to install django-patterns?

tranhieutt/software_development_department/django-patterns

$npx -y skills add tranhieutt/software_development_department --skill django-patterns

Installs into the current project.

Summary

Provides expert-level Django development patterns covering App Router (indirectly via REST/GraphQL), async views, DRF, Celery, signals, middleware, and performance optimization. Use when building complex Django 5.x applications or identifying N+1 query issues.

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SKILL.md

1	# Django & DRF Professional Patterns
2
3	## Core Expertise
4	- Modern Django: 5.x features, async views/middleware, ASGI deployment.
5	- Background & Real-time: Celery integration, Django Channels.
6	- ORM Optimization: select_related, prefetch_related, custom managers.
7	- Security: JWT auth, OAuth2, RBAC, protection against SQLi/XSS/CSRF.
8
9	## Critical rules (non-obvious)
10
11	- N+1 queries: always use `select_related` (FK) / `prefetch_related` (M2M) — never iterate and query inside loops
12	- `get_or_create` race condition: wrap in `transaction.atomic()` in concurrent environments
13	- Never call `save()` inside `pre_save` signal — causes infinite recursion; use `update_fields`
14	- `bulk_create` skips signals and `save()` — don't use when signal logic is required
15	- Migrations on large tables: use `RunSQL` with `CONCURRENTLY` index creation to avoid locks
16
17	## ORM: select_related vs prefetch_related
18
19	```python
20	# FK / OneToOne → select_related (JOIN)
21	books = Book.objects.select_related("author", "author__publisher").all()
22
23	# M2M / reverse FK → prefetch_related (separate query)
24	authors = Author.objects.prefetch_related("books", "books__tags").all()
25
26	# Custom prefetch with queryset
27	from django.db.models import Prefetch
28	Author.objects.prefetch_related(
29	Prefetch("books", queryset=Book.objects.filter(published=True), to_attr="active_books")
30	)
31	```
32
33	## ORM: annotations and aggregations
34
35	```python
36	from django.db.models import Count, Avg, Q, F, Value
37	from django.db.models.functions import Coalesce
38
39	Author.objects.annotate(
40	book_count=Count("books"),
41	avg_rating=Coalesce(Avg("books__rating"), Value(0.0)),
42	high_rated=Count("books", filter=Q(books__rating__gte=4)),
43	).filter(book_count__gt=0).order_by("-book_count")
44	```
45
46	## ORM: F expressions (avoid race conditions)
47
48	```python
49	# BAD — race condition
50	product = Product.objects.get(pk=pk)
51	product.stock -= quantity
52	product.save()
53
54	# GOOD — atomic at DB level
55	Product.objects.filter(pk=pk).update(stock=F("stock") - quantity)
56	```
57
58	## Views: class-based view pattern
59
60	```python
61	from django.views import View
62	from django.contrib.auth.mixins import LoginRequiredMixin
63
64	class OrderDetailView(LoginRequiredMixin, View):
65	def get(self, request, pk):
66	order = get_object_or_404(Order.objects.select_related("user"), pk=pk, user=request.user)
67	return JsonResponse(OrderSerializer(order).data)
68	```
69
70	## DRF: serializer with validation
71
72	```python
73	class ProductSerializer(serializers.ModelSerializer):
74	class Meta:
75	model = Product
76	fields = ["id", "name", "price", "stock"]
77	read_only_fields = ["id"]
78
79	def validate_price(self, value):
80	if value <= 0:
81	raise serializers.ValidationError("Price must be positive.")
82	return value
83
84	def validate(self, data): # cross-field
85	if data["stock"] == 0 and data.get("is_featured"):
86	raise serializers.ValidationError("Out-of-stock products cannot be featured.")
87	return data
88	```
89
90	## DRF: ViewSet with custom actions
91
92	```python
93	from rest_framework import viewsets, status
94	from rest_framework.decorators import action
95	from rest_framework.response import Response
96
97	class ProductViewSet(viewsets.ModelViewSet):
98	queryset = Product.objects.select_related("category")
99	serializer_class = ProductSerializer
100	permission_classes = [IsAuthenticated]
101
102	@action(detail=True, methods=["post"], url_path="archive")
103	def archive(self, request, pk=None):
104	product = self.get_object()
105	product.is_archived = True
106	product.save(update_fields=["is_archived"])
107	return Response(status=status.HTTP_204_NO_CONTENT)
108	```
109
110	## DRF: filtering + pagination
111
112	```python
113	# settings.py
114	REST_FRAMEWORK = {
115	"DEFAULT_FILTER_BACKENDS": ["django_filters.rest_framework.DjangoFilterBackend"],
116	"DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.CursorPagination",
117	"PAGE_SIZE": 20,
118	}
119
120	# viewset
121	class ProductViewSet(viewsets.ReadOnlyModelViewSet):
122	filterset_fields = {"price": ["gte", "lte"], "category": ["exact"]}
123	ordering_fields = ["price", "created_at"]
124	search_fields = ["name", "description"]
125	```
126
127	## Celery task pattern
128
129	```python
130	from celery import shared_task
131	from django.db import transaction
132
133	@shared_task(bind=True, max_retries=3, default_retry_delay=60)
134	def send_order_email(self

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django-patterns

69stars41forks

View on GitHub

How to install django-patterns?

tranhieutt/software_development_department/django-patterns

$npx -y skills add tranhieutt/software_development_department --skill django-patterns

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Django & DRF Professional Patterns
2
3	## Core Expertise
4	- Modern Django: 5.x features, async views/middleware, ASGI deployment.
5	- Background & Real-time: Celery integration, Django Channels.
6	- ORM Optimization: select_related, prefetch_related, custom managers.
7	- Security: JWT auth, OAuth2, RBAC, protection against SQLi/XSS/CSRF.
8
9	## Critical rules (non-obvious)
10
11	- N+1 queries: always use `select_related` (FK) / `prefetch_related` (M2M) — never iterate and query inside loops
12	- `get_or_create` race condition: wrap in `transaction.atomic()` in concurrent environments
13	- Never call `save()` inside `pre_save` signal — causes infinite recursion; use `update_fields`
14	- `bulk_create` skips signals and `save()` — don't use when signal logic is required
15	- Migrations on large tables: use `RunSQL` with `CONCURRENTLY` index creation to avoid locks
16
17	## ORM: select_related vs prefetch_related
18
19	```python
20	# FK / OneToOne → select_related (JOIN)
21	books = Book.objects.select_related("author", "author__publisher").all()
22
23	# M2M / reverse FK → prefetch_related (separate query)
24	authors = Author.objects.prefetch_related("books", "books__tags").all()
25
26	# Custom prefetch with queryset
27	from django.db.models import Prefetch
28	Author.objects.prefetch_related(
29	Prefetch("books", queryset=Book.objects.filter(published=True), to_attr="active_books")
30	)
31	```
32
33	## ORM: annotations and aggregations
34
35	```python
36	from django.db.models import Count, Avg, Q, F, Value
37	from django.db.models.functions import Coalesce
38
39	Author.objects.annotate(
40	book_count=Count("books"),
41	avg_rating=Coalesce(Avg("books__rating"), Value(0.0)),
42	high_rated=Count("books", filter=Q(books__rating__gte=4)),
43	).filter(book_count__gt=0).order_by("-book_count")
44	```
45
46	## ORM: F expressions (avoid race conditions)
47
48	```python
49	# BAD — race condition
50	product = Product.objects.get(pk=pk)
51	product.stock -= quantity
52	product.save()
53
54	# GOOD — atomic at DB level
55	Product.objects.filter(pk=pk).update(stock=F("stock") - quantity)
56	```
57
58	## Views: class-based view pattern
59
60	```python
61	from django.views import View
62	from django.contrib.auth.mixins import LoginRequiredMixin
63
64	class OrderDetailView(LoginRequiredMixin, View):
65	def get(self, request, pk):
66	order = get_object_or_404(Order.objects.select_related("user"), pk=pk, user=request.user)
67	return JsonResponse(OrderSerializer(order).data)
68	```
69
70	## DRF: serializer with validation
71
72	```python
73	class ProductSerializer(serializers.ModelSerializer):
74	class Meta:
75	model = Product
76	fields = ["id", "name", "price", "stock"]
77	read_only_fields = ["id"]
78
79	def validate_price(self, value):
80	if value <= 0:
81	raise serializers.ValidationError("Price must be positive.")
82	return value
83
84	def validate(self, data): # cross-field
85	if data["stock"] == 0 and data.get("is_featured"):
86	raise serializers.ValidationError("Out-of-stock products cannot be featured.")
87	return data
88	```
89
90	## DRF: ViewSet with custom actions
91
92	```python
93	from rest_framework import viewsets, status
94	from rest_framework.decorators import action
95	from rest_framework.response import Response
96
97	class ProductViewSet(viewsets.ModelViewSet):
98	queryset = Product.objects.select_related("category")
99	serializer_class = ProductSerializer
100	permission_classes = [IsAuthenticated]
101
102	@action(detail=True, methods=["post"], url_path="archive")
103	def archive(self, request, pk=None):
104	product = self.get_object()
105	product.is_archived = True
106	product.save(update_fields=["is_archived"])
107	return Response(status=status.HTTP_204_NO_CONTENT)
108	```
109
110	## DRF: filtering + pagination
111
112	```python
113	# settings.py
114	REST_FRAMEWORK = {
115	"DEFAULT_FILTER_BACKENDS": ["django_filters.rest_framework.DjangoFilterBackend"],
116	"DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.CursorPagination",
117	"PAGE_SIZE": 20,
118	}
119
120	# viewset
121	class ProductViewSet(viewsets.ReadOnlyModelViewSet):
122	filterset_fields = {"price": ["gte", "lte"], "category": ["exact"]}
123	ordering_fields = ["price", "created_at"]
124	search_fields = ["name", "description"]
125	```
126
127	## Celery task pattern
128
129	```python
130	from celery import shared_task
131	from django.db import transaction
132
133	@shared_task(bind=True, max_retries=3, default_retry_delay=60)
134	def send_order_email(self

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