Agent skill

django-simplifier

Simplify overly complex Django code and detect Django-specific anti-patterns. Use when user asks to simplify, refactor, or improve Django code, find N+1 queries, detect Django anti-patterns, optimize QuerySets, or analyze Django project architecture. Triggers on requests involving Django models, views, QuerySets, ORM optimization, serializers, forms, signals, middleware, or Django best practices. For general Python analysis, use the python-simplifier skill instead.

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Install this agent skill to your Project

npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/data/django-simplifier

SKILL.md

Django Code Simplifier

Transform complex Django code into clean, performant, idiomatic solutions.

Analysis Scripts

bash
# Comprehensive Django analysis (runs all Django checks)
python scripts/analyze_django.py /path/to/project

# Individual analyzers:
python scripts/find_django_issues.py .           # N+1 queries, fat views, basic issues
python scripts/find_django_antipatterns.py .     # ORM misuse, security issues, model problems
python scripts/find_django_overengineering.py .  # Unnecessary abstractions, premature patterns

# Filter by category or severity:
python scripts/find_django_antipatterns.py . --category performance
python scripts/find_django_antipatterns.py . --category security
python scripts/find_django_antipatterns.py . --min-severity medium

# JSON output for CI/tooling
python scripts/analyze_django.py . --format json > report.json

What Each Script Detects

find_django_issues.py - Basic Issues

  • N+1 query risks (.all() in loops)
  • .save() / .delete() / .create() in loops
  • Fat views (100+ lines)
  • Hardcoded URLs instead of reverse()
  • Missing select_related / prefetch_related

find_django_antipatterns.py - Comprehensive Anti-Patterns

Category Issues Detected
query save_in_loop, create_in_loop, unbounded_queryset, update_without_f, raw_sql, deprecated_extra
performance excessive_queries, nested template loops, template queries
model missing_str_method, fat_model, too_many_fields
view hardcoded_url, fat_view_method, url_without_name
form query_in_form_clean
security hardcoded_secret, debug_true, mark_safe_usage, eval_exec_usage

find_django_overengineering.py - Over-Engineering

Issue Description
single_impl_abstract_model Abstract model with only one concrete child
unused_abstract_model Abstract model never extended
unnecessary_manager Custom manager with ≤1 method
unnecessary_signal Signal for simple save logic
single_use_mixin Mixin used only once
deep_form_inheritance Form/Serializer with 3+ inheritance levels
unnecessary_middleware Middleware with minimal logic
unnecessary_service_layer Service wrapping simple CRUD

Common Django Patterns

N+1 Query Prevention

python
# Before: N+1 problem
for order in Order.objects.all():
    print(order.customer.name)  # Query per iteration!

# After: select_related (ForeignKey/OneToOne)
for order in Order.objects.select_related('customer'):
    print(order.customer.name)  # Single query

# After: prefetch_related (ManyToMany/reverse FK)
for customer in Customer.objects.prefetch_related('orders'):
    print(customer.orders.count())

Bulk Operations

python
# Before: Loop creates (N queries)
for data in items:
    Model.objects.create(**data)

# After: bulk_create (1 query)
Model.objects.bulk_create([Model(**d) for d in items])

# Before: Loop updates
for obj in queryset:
    obj.status = 'done'
    obj.save()

# After: Single update
queryset.update(status='done')

# With F() for safe increment
from django.db.models import F
Product.objects.filter(id=1).update(stock=F('stock') - 1)

Fat View → Thin View

python
# Before: Business logic in view
def order_view(request, order_id):
    order = Order.objects.get(id=order_id)
    # 50 lines of business logic...
    return render(...)

# After: Logic in model/service
def order_view(request, order_id):
    order = get_object_or_404(Order, id=order_id)
    result = order.process()  # Logic moved to model
    return render(request, 'order.html', {'result': result})

Signals → Explicit Methods

python
# Before: Hidden signal
@receiver(post_save, sender=Order)
def update_inventory(sender, instance, **kwargs):
    # Hard to trace, implicit behavior
    ...

# After: Explicit method
class Order(models.Model):
    def complete(self):
        self.status = 'completed'
        self.save()
        self._update_inventory()  # Explicit, traceable

URL Best Practices

python
# Before: Hardcoded
return redirect('/orders/123/')

# After: Named URL
from django.urls import reverse
return redirect(reverse('order-detail', args=[123]))

# Or with shortcut
from django.shortcuts import redirect
return redirect('order-detail', pk=123)

Model Best Practices

python
class Order(models.Model):
    # Always add __str__
    def __str__(self):
        return f"Order #{self.number}"
    
    # Use TextChoices
    class Status(models.TextChoices):
        PENDING = 'pending', 'Pending'
        COMPLETED = 'completed', 'Completed'
    
    status = models.CharField(max_length=20, choices=Status.choices)
    
    # Don't use null=True on CharField
    # BAD: name = models.CharField(null=True, blank=True)
    # GOOD:
    name = models.CharField(blank=True, default='')
    
    # Always set related_name
    customer = models.ForeignKey(Customer, related_name='orders', on_delete=models.CASCADE)
    
    class Meta:
        ordering = ['-created_at']
        indexes = [models.Index(fields=['status', 'created_at'])]

Django Over-Engineering Signs

Pattern Problem Solution
Abstract model with 1 child Premature abstraction Merge into concrete model
CBV with 6+ overrides Too complex Use function-based view
Single-use mixin No reuse benefit Inline the code
Many signal handlers Hard to trace Use explicit method calls
Custom manager for simple filter Unnecessary Use QuerySet methods
Service layer for CRUD Extra indirection Use model methods

Security Checklist

python
# Use get_object_or_404 with ownership check
order = get_object_or_404(Order, id=id, owner=request.user)

# Never use mark_safe with user data
# BAD: mark_safe(user_input)
# GOOD:
from django.utils.html import format_html
format_html('<p>{}</p>', user_input)

# Keep secrets out of code
# BAD: SECRET_KEY = 'hardcoded-secret'
# GOOD: SECRET_KEY = os.environ.get('SECRET_KEY')

When to Use What

Need Use
Simple CRUD Generic views, ModelForm
Complex business logic Model methods
Cross-cutting concerns Middleware (sparingly)
Decoupled apps Signals (sparingly)
Query optimization select_related, prefetch_related
Bulk operations bulk_create, bulk_update, update()

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