Feature/query optimization

[malikabdullahnaazar]

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Description

This PR adds automatic query optimization capabilities to Django REST Framework, helping developers prevent N+1 query problems by automatically analyzing serializer fields and applying select_related() and prefetch_related() optimizations.

Problem Statement

N+1 query problems are one of the most common performance issues in Django REST Framework applications. Developers often forget to optimize querysets when using serializers with related fields, leading to:

• Multiple database queries for related objects
• Degraded API performance
• Increased database load
• Poor user experience

Currently, DRF requires developers to manually optimize querysets in get_queryset() methods, which is error-prone and easy to forget.

Solution

This feature provides:

1. Automatic Query Analysis: Analyzes serializer fields to detect relationships
2. Automatic Optimization: Applies select_related() and prefetch_related() automatically
3. N+1 Detection: Warns developers about potential N+1 queries in development
4. Easy Integration: Simple mixin-based API for viewsets

Implementation Details

New Module: rest_framework.optimization

Core Components:

1. query_analyzer.py:

   • QueryAnalyzer class: Analyzes serializer fields to detect relationships
   • detect_n_plus_one(): Detects potential N+1 queries in querysets

2. optimizer.py:

   • optimize_queryset(): Applies query optimizations to querysets
   • analyze_serializer_fields(): Analyzes serializer for optimization needs
   • get_optimization_suggestions(): Provides code examples for optimization

3. mixins.py:

   • OptimizedQuerySetMixin: Mixin for automatic query optimization in viewsets

4. middleware.py:

   • QueryOptimizationMiddleware: Optional middleware for development-time N+1 detection

Settings

Added two new settings to REST_FRAMEWORK:

• ENABLE_QUERY_OPTIMIZATION: Enable/disable automatic optimization (default: True)
• WARN_ON_N_PLUS_ONE: Show warnings when N+1 queries detected (default: None, auto-detects based on DEBUG)

Tests

• Comprehensive test suite in tests/test_optimization.py
• All tests passing
• Covers edge cases and error handling

Usage Examples

Basic Usage

from rest_framework import viewsets
from rest_framework.optimization import OptimizedQuerySetMixin

class BookViewSet(OptimizedQuerySetMixin, viewsets.ModelViewSet):
    queryset = Book.objects.all()
    serializer_class = BookSerializer
    # Automatically optimizes with select_related('author') and prefetch_related('tags')

Manual Optimization

from rest_framework.optimization import optimize_queryset

queryset = Book.objects.all()
optimized = optimize_queryset(queryset, BookSerializer)

Explicit Fields

class BookViewSet(OptimizedQuerySetMixin, viewsets.ModelViewSet):
    queryset = Book.objects.all()
    serializer_class = BookSerializer
    select_related_fields = ['author', 'category']
    prefetch_related_fields = ['tags']

Features

✅ Automatic Field Detection

• Detects ForeignKey and OneToOneField relationships → uses select_related()
• Detects ManyToManyField and reverse relationships → uses prefetch_related()
• Handles nested serializers recursively
• Works with custom field definitions (e.g., PrimaryKeyRelatedField(many=True))

✅ Smart Optimization

• Merges explicit and auto-detected fields
• Avoids duplicate optimizations
• Handles existing queryset optimizations gracefully
• Works with empty querysets and non-queryset objects

✅ Development Warnings

• Detects potential N+1 queries
• Provides helpful warning messages
• Only active in DEBUG mode by default
• Can be explicitly enabled/disabled

Code Quality

✅ Follows DRF Standards

• No type hints (matches DRF codebase style)
• Proper docstrings following DRF conventions
• Uses DRF's internal utilities (model_meta.get_field_info)
• Follows DRF naming conventions
• Proper error handling

✅ Testing

• Comprehensive test coverage
• Tests for all major features
• Edge case testing
• Performance testing
• All tests passing

Backward Compatibility

• ✅ Fully backward compatible
• ✅ Opt-in feature (enabled by default but can be disabled)
• ✅ Doesn't break existing code
• ✅ Works with all existing DRF features

Performance Impact

• Minimal overhead: Analysis happens once per serializer class
• Cached results: Analysis results are cached
• No impact on production if disabled
• Significant performance improvement when enabled

Files Changed

New Files:

• rest_framework/optimization/__init__.py
• rest_framework/optimization/query_analyzer.py
• rest_framework/optimization/optimizer.py
• rest_framework/optimization/mixins.py
• rest_framework/optimization/middleware.py
• tests/test_optimization.py

Modified Files:

• rest_framework/settings.py (added optimization settings)

Breaking Changes

None. This is a purely additive feature.

Migration Guide

No migration needed. The feature works out of the box:

1. Import the mixin
2. Add it to your viewset
3. Done!

Checklist

• Code follows DRF style guidelines
• All tests passing
• Backward compatible
• No breaking changes
• Proper error handling
• Edge cases handled
• Performance tested
• Code reviewed for best practices

Notes

This feature addresses one of the top 3 most common issues developers face with DRF (N+1 query problems). While DRF is considered feature-complete, this enhancement significantly improves developer experience and application performance without breaking existing functionality.