Django REST Framework patterns. Trigger: When implementing generic DRF APIs (ViewSets, serializers, routers, permissions, filtersets). For Prowler API specifics (RLS/RBAC/Providers), also use prowler-api.
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---
name: django-drf
description: >
Django REST Framework patterns.
Trigger: When implementing generic DRF APIs (ViewSets, serializers, routers, permissions, filtersets). For Prowler API specifics (RLS/RBAC/Providers), also use prowler-api.
license: Apache-2.0
metadata:
author: prowler-cloud
version: "1.2.0"
scope: [root, api]
auto_invoke:
- "Creating ViewSets, serializers, or filters in api/"
- "Implementing JSON:API endpoints"
- "Adding DRF pagination or permissions"
allowed-tools: Read, Edit, Write, Glob, Grep, Bash, WebFetch, WebSearch, Task
---
## Critical Patterns
- ALWAYS separate serializers by operation: Read / Create / Update / Include
- ALWAYS use `filterset_class` for complex filtering (not `filterset_fields`)
- ALWAYS validate unknown fields in write serializers (inherit `BaseWriteSerializer`)
- ALWAYS use `select_related`/`prefetch_related` in `get_queryset()` to avoid N+1
- ALWAYS handle `swagger_fake_view` in `get_queryset()` for schema generation
- ALWAYS use `@extend_schema_field` for OpenAPI docs on `SerializerMethodField`
- NEVER put business logic in serializers - use services/utils
- NEVER use auto-increment PKs - use UUIDv4 or UUIDv7
- NEVER use trailing slashes in URLs (`trailing_slash=False`)
> **Note:** `swagger_fake_view` is specific to **drf-spectacular** for OpenAPI schema generation.
---
## Implementation Checklist
When implementing a new endpoint, review these patterns in order:
| # | Pattern | Reference | Key Points |
|---|---------|-----------|------------|
| 1 | **Models** | `api/models.py` | UUID PK, `inserted_at`/`updated_at`, `JSONAPIMeta.resource_name` |
| 2 | **ViewSets** | `api/base_views.py`, `api/v1/views.py` | Inherit `BaseRLSViewSet`, `get_queryset()` with N+1 prevention |
| 3 | **Serializers** | `api/v1/serializers.py` | Separate Read/Create/Update/Include, inherit `BaseWriteSerializer` |
| 4 | **Filters** | `api/filters.py` | Use `filterset_class`, inherit base filter classes |
| 5 | **Permissions** | `api/base_views.py` | `required_permissions`, `set_required_permissions()` |
| 6 | **Pagination** | `api/pagination.py` | Custom pagination class if needed |
| 7 | **URL Routing** | `api/v1/urls.py` | `trailing_slash=False`, kebab-case paths |
| 8 | **OpenAPI Schema** | `api/v1/views.py` | `@extend_schema_view` with drf-spectacular |
| 9 | **Tests** | `api/tests/test_views.py` | JSON:API content type, fixture patterns |
> **Full file paths**: See [references/file-locations.md](references/file-locations.md)
---
## Decision Trees
### Which Serializer?
```
GET list/retrieve → <Model>Serializer
POST create → <Model>CreateSerializer
PATCH update → <Model>UpdateSerializer
?include=... → <Model>IncludeSerializer
```
### Which Base Serializer?
```
Read-only serializer → BaseModelSerializerV1
Create with tenant_id → RLSSerializer + BaseWriteSerializer (auto-injects tenant_id on create)
Update with validation → BaseWriteSerializer (tenant_id already exists on object)
Non-model data → BaseSerializerV1
```
### Which Filter Base?
```
Direct FK to Provider → BaseProviderFilter
FK via Scan → BaseScanProviderFilter
No provider relation → FilterSet
```
### Which Base ViewSet?
```
RLS-protected model → BaseRLSViewSet (most common)
Tenant operations → BaseTenantViewset
User operations → BaseUserViewset
No RLS required → BaseViewSet (rare)
```
### Resource Name Format?
```
Single word model → plural lowercase (Provider → providers)
Multi-word model → plural lowercase kebab (ProviderGroup → provider-groups)
Through/join model → parent-child pattern (UserRoleRelationship → user-roles)
Aggregation/overview → descriptive kebab plural (ComplianceOverview → compliance-overviews)
```
---
## Serializer Patterns
### Base Class Hierarchy
```python
# Read serializer (most common)
class ProviderSerializer(RLSSerializer):
class Meta:
model = Provider
fields = ["id", "provider", "uid", "alias", "connected", "inserted_at"]
# Write serializer (validates unknown fields)
class ProviderCreateSerializer(RLSSerializer, BaseWriteSerializer):
class Meta:
model = Provider
fields = ["provider", "uid", "alias"]
# Include serializer (sparse fields for ?include=)
class ProviderIncludeSerializer(RLSSerializer):
class Meta:
model = Provider
fields = ["id", "alias"] # Minimal fields
```
### SerializerMethodField with OpenAPI
```python
from drf_spectacular.utils import extend_schema_field
class ProviderSerializer(RLSSerializer):
connection = serializers.SerializerMethodField(read_only=True)
@extend_schema_field({
"type": "object",
"properties": {
"connected": {"type": "boolean"},
"last_checked_at": {"type": "string", "format": "date-time"},
},
})
def get_connection(self, obj):
return {
"connected": obj.connected,
"last_checked_at": obj.connection_last_checked_at,
}
```
### Included Serializers (JSON:API)
```python
class ScanSerializer(RLSSerializer):
included_serializers = {
"provider": "api.v1.serializers.ProviderIncludeSerializer",
}
```
### Sensitive Data Masking
```python
def to_representation(self, instance):
data = super().to_representation(instance)
# Mask by default, expose only on explicit request
fields_param = self.context.get("request").query_params.get("fields[my-model]", "")
if "api_key" in fields_param:
data["api_key"] = instance.api_key_decoded
else:
data["api_key"] = "****" if instance.api_key else None
return data
```
---
## ViewSet Patterns
### get_queryset() with N+1 Prevention
**Always combine** `swagger_fake_view` check with `select_related`/`prefetch_related`:
```python
def get_queryset(self):
# REQUIRED: Return empty queryset for OpenAPI schema generation
if getattr(self, "swagger_fake_view", False):
return Provider.objects.none()
# N+1 prevention: eager load relationships
return Provider.objects.select_related(
"tenant",
).prefetch_related(
"provider_groups",
Prefetch("tags", queryset=ProviderTag.objects.filter(tenant_id=self.request.tenant_id)),
)
```
> **Why swagger_fake_view?** drf-spectacular introspects ViewSets to generate OpenAPI schemas. Without this check, it executes real queries and can fail without request context.
### Action-Specific Serializers
```python
def get_serializer_class(self):
if self.action == "create":
return ProviderCreateSerializer
elif self.action == "partial_update":
return ProviderUpdateSerializer
elif self.action in ["connection", "destroy"]:
return TaskSerializer
return ProviderSerializer
```
### Dynamic Permissions per Action
```python
class ProviderViewSet(BaseRLSViewSet):
required_permissions = [Permissions.MANAGE_PROVIDERS]
def set_required_permissions(self):
if self.action in ["list", "retrieve"]:
self.required_permissions = [] # Read-only = no permission
else:
self.required_permissions = [Permissions.MANAGE_PROVIDERS]
```
### Cache Decorator
```python
from django.utils.decorators import method_decorator
from django.views.decorators.cache import cache_control
CACHE_DECORATOR = cache_control(
max_age=django_settings.CACHE_MAX_AGE,
stale_while_revalidate=django_settings.CACHE_STALE_WHILE_REVALIDATE,
)
@method_decorator(CACHE_DECORATOR, name="list")
@method_decorator(CACHE_DECORATOR, name="retrieve")
class ProviderViewSet(BaseRLSViewSet):
pass
```
### Custom Actions
```python
# Detail action (operates on single object)
@action(detail=True, methods=["post"], url_name="connection")
def connection(self, request, pk=None):
instance = self.get_object()
# Process instance...
# List action (operates on collection)
@action(detail=False, methods=["get"], url_name="metadata")
def metadata(self, request):
queryset = self.filter_queryset(self.get_queryset())
# Aggregate over queryset...
```
---
## Filter Patterns
### Base Filter Classes
```python
class BaseProviderFilter(FilterSet):
"""For models with direct FK to Provider"""
provider_id = UUIDFilter(field_name="provider__id", lookup_expr="exact")
provider_id__in = UUIDInFilter(field_name="provider__id", lookup_expr="in")
provider_type = ChoiceFilter(field_name="provider__provider", choices=Provider.ProviderChoices.choices)
class BaseScanProviderFilter(FilterSet):
"""For models with FK to Scan (Scan has FK to Provider)"""
provider_id = UUIDFilter(field_name="scan__provider__id", lookup_expr="exact")
```
### Custom Multi-Value Filters
```python
class UUIDInFilter(BaseInFilter, UUIDFilter):
pass
class CharInFilter(BaseInFilter, CharFilter):
pass
class ChoiceInFilter(BaseInFilter, ChoiceFilter):
pass
```
### ArrayField Filtering
```python
# Single value contains
region = CharFilter(method="filter_region")
def filter_region(self, queryset, name, value):
return queryset.filter(resource_regions__contains=[value])
# Multi-value overlap
region__in = CharInFilter(field_name="resource_regions", lookup_expr="overlap")
```
### Date Range Validation
```python
def filter_queryset(self, queryset):
# Require date filter for performance
if not (date_filters_provided):
raise ValidationError([{
"detail": "At least one date filter is required",
"status": 400,
"source": {"pointer": "/data/attributes/inserted_at"},
"code": "required",
}])
# Validate max range
if date_range > settings.FINDINGS_MAX_DAYS_IN_RANGE:
raise ValidationError(...)
return super().filter_queryset(queryset)
```
### Dynamic FilterSet Selection
```python
def get_filterset_class(self):
if self.action in ["latest", "metadata_latest"]:
return LatestFindingFilter
return FindingFilter
```
### Enum Field Override
```python
class Meta:
model = Finding
filter_overrides = {
FindingDeltaEnumField: {"filter_class": CharFilter},
StatusEnumField: {"filter_class": CharFilter},
SeverityEnumField: {"filter_class": CharFilter},
}
```
---
## Performance Patterns
### PaginateByPkMixin
For large querysets with expensive joins:
```python
class PaginateByPkMixin:
def paginate_by_pk(self, request, base_queryset, manager,
select_related=None, prefetch_related=None):
# 1. Get PKs only (cheap)
pk_list = base_queryset.values_list("id", flat=True)
page = self.paginate_queryset(pk_list)
# 2. Fetch full objects for just the page
queryset = manager.filter(id__in=page)
if select_related:
queryset = queryset.select_related(*select_related)
if prefetch_related:
queryset = queryset.prefetch_related(*prefetch_related)
# 3. Re-sort to preserve DB ordering
queryset = sorted(queryset, key=lambda obj: page.index(obj.id))
return self.get_paginated_response(self.get_serializer(queryset, many=True).data)
```
### Prefetch in Serializers
```python
def get_tags(self, obj):
# Use prefetched tags if available
if hasattr(obj, "prefetched_tags"):
return {tag.key: tag.value for tag in obj.prefetched_tags}
# Fallback (causes N+1 if not prefetched)
return obj.get_tags(self.context.get("tenant_id"))
```
---
## Naming Conventions
| Entity | Pattern | Example |
|--------|---------|---------|
| Serializer (read) | `<Model>Serializer` | `ProviderSerializer` |
| Serializer (create) | `<Model>CreateSerializer` | `ProviderCreateSerializer` |
| Serializer (update) | `<Model>UpdateSerializer` | `ProviderUpdateSerializer` |
| Serializer (include) | `<Model>IncludeSerializer` | `ProviderIncludeSerializer` |
| Filter | `<Model>Filter` | `ProviderFilter` |
| ViewSet | `<Model>ViewSet` | `ProviderViewSet` |
---
## OpenAPI Documentation
```python
from drf_spectacular.utils import extend_schema, extend_schema_view
@extend_schema_view(
list=extend_schema(tags=["Provider"], summary="List all providers"),
retrieve=extend_schema(tags=["Provider"], summary="Retrieve provider"),
create=extend_schema(tags=["Provider"], summary="Create provider"),
)
@extend_schema(tags=["Provider"])
class ProviderViewSet(BaseRLSViewSet):
pass
```
---
## API Security Patterns
> **Full examples**: See [assets/security_patterns.py](assets/security_patterns.py)
| Pattern | Key Points |
|---------|------------|
| **Input Validation** | Use `validate_<field>()` for sanitization, `validate()` for cross-field |
| **Prevent Mass Assignment** | ALWAYS use explicit `fields` list, NEVER `__all__` or `exclude` |
| **Object-Level Permissions** | Implement `has_object_permission()` for ownership checks |
| **Rate Limiting** | Configure `DEFAULT_THROTTLE_RATES`, use per-view throttles for sensitive endpoints |
| **Prevent Info Disclosure** | Generic error messages, return 404 not 403 for unauthorized (prevents enumeration) |
| **SQL Injection** | ALWAYS use ORM parameterization, NEVER string interpolation in raw SQL |
### Quick Reference
```python
# Input validation in serializer
def validate_uid(self, value):
value = value.strip().lower()
if not re.match(r'^[a-z0-9-]+$', value):
raise serializers.ValidationError("Invalid format")
return value
# Explicit fields (prevent mass assignment)
class Meta:
fields = ["name", "email"] # GOOD: whitelist
read_only_fields = ["id", "inserted_at"] # System fields
# Object permission
class IsOwnerOrReadOnly(BasePermission):
def has_object_permission(self, request, view, obj):
if request.method in SAFE_METHODS:
return True
return obj.owner == request.user
# Throttling for sensitive endpoints
class BurstRateThrottle(UserRateThrottle):
rate = "10/minute"
# Safe error messages (prevent enumeration)
def get_object(self):
try:
return super().get_object()
except Http404:
raise NotFound("Resource not found") # Generic, no internal IDs
```
---
## Commands
```bash
# Development
cd api && poetry run python src/backend/manage.py runserver
cd api && poetry run python src/backend/manage.py shell
# Database
cd api && poetry run python src/backend/manage.py makemigrations
cd api && poetry run python src/backend/manage.py migrate
# Testing
cd api && poetry run pytest -x --tb=short
cd api && poetry run make lint
```
---
## Resources
### Local References
- **File Locations**: See [references/file-locations.md](references/file-locations.md)
- **JSON:API Conventions**: See [references/json-api-conventions.md](references/json-api-conventions.md)
- **Security Patterns**: See [assets/security_patterns.py](assets/security_patterns.py)
### Context7 MCP (Recommended)
**Prerequisite:** Install Context7 MCP server for up-to-date documentation lookup.
When implementing or debugging, query these libraries via `mcp_context7_query-docs`:
| Library | Context7 ID | Use For |
|---------|-------------|---------|
| **Django** | `/websites/djangoproject_en_5_2` | Models, ORM, migrations |
| **DRF** | `/websites/django-rest-framework` | ViewSets, serializers, permissions |
| **drf-spectacular** | `/tfranzel/drf-spectacular` | OpenAPI schema, `@extend_schema` |
**Example queries:**
```
mcp_context7_query-docs(libraryId="/websites/django-rest-framework", query="ViewSet get_queryset best practices")
mcp_context7_query-docs(libraryId="/tfranzel/drf-spectacular", query="extend_schema examples for custom actions")
mcp_context7_query-docs(libraryId="/websites/djangoproject_en_5_2", query="model constraints and indexes")
```
> **Note:** Use `mcp_context7_resolve-library-id` first if you need to find the correct library ID.
### External Docs
- **DRF Docs**: https://www.django-rest-framework.org/
- **DRF JSON:API**: https://django-rest-framework-json-api.readthedocs.io/
- **drf-spectacular**: https://drf-spectacular.readthedocs.io/
- **django-filter**: https://django-filter.readthedocs.io/