django-query-guard 🛡️

Created by:

Atiqur Rahman
Software QA Engineer | SDET | Test Automation Architect | Microsoft Contributor | Open Source Contributor
📍 Dhaka, Bangladesh | ✉️ rahman.atiqur.pro@gmail.com | 🌐 LinkedIn | 🐙 GitHub Profile

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Stop N+1 database queries before they hit production.
django-query-guard is an ultra-fast, zero-dependency Python & Pytest plugin that automatically detects N+1 queries and enforces strict query count limits in your Django test suites and backend code.

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💡 Why Django Developers Need This

In Django, the ORM makes database queries so easy that it’s terrifyingly easy to accidentally write N+1 queries:

# ❌ THE N+1 ACCIDENT
# Fetches 100 users, then executes 100 individual queries for each profile!
# Total: 101 Database Queries! 🐌
users = User.objects.all()
profiles = [user.profile.bio for user in users]

The Solution: django-query-guard

Instead of relying on manual code reviews or checking server logs, django-query-guard turns query limits and N+1 prevention into automated, enforceable CI/CD tests:

# ✅ THE SOLUTION
import pytest

@pytest.mark.django_db
@pytest.mark.query_guard(max_queries=2, detect_n_plus_one=True)
def test_user_profiles_api(client):
    response = client.get("/api/users/")
    assert response.status_code == 200

If your endpoint accidentally runs 101 queries instead of 2, Pytest fails instantly with an exact breakdown of which query repeated! 💥

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🔥 Key Features

• 🎯 Pytest Marker Integration: Simple @pytest.mark.query_guard(max_queries=N).
• 🧠 Smart SQL Normalization: Normalizes SQL queries (e.g. WHERE id = 1 and WHERE id = 2 are recognized as the exact same query pattern).
• 🛡️ Zero Heavy Dependencies: Built purely on Django's native database execution wrapper and standard library.
• ⚡ Ultra-Fast: Sub-millisecond execution overhead (< 1ms per test).
• 🐍 Python 3.10+ & Django 4.0+ Compatible: Works out-of-the-box with all modern Django versions.

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📦 Installation

Install django-query-guard via pip:

pip install django-query-guard

For development and testing with Pytest:

pip install django-query-guard[dev]

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📖 A to Z Guide: How to Use

1. Using @pytest.mark.query_guard in Pytest

Simply decorate any test function that accesses the database:

import pytest

@pytest.mark.django_db
@pytest.mark.query_guard(max_queries=3)
def test_fetch_dashboard_data(client):
    response = client.get("/api/dashboard/")
    assert response.status_code == 200

Parameters for query_guard Marker:

Parameter	Type	Default	Description
max_queries	int	None	Maximum allowed total SQL queries. Raises QueryCountExceededError if exceeded.
detect_n_plus_one	bool	True	Automatically detect N+1 query patterns.
n_plus_one_threshold	int	2	Minimum repetitions of a normalized query required to trigger N+1 detection.

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2. Strict N+1 Detection Mode

Even if your total query count is under max_queries, a loop executing duplicate queries will trigger an NPlusOneQueryError:

@pytest.mark.django_db
@pytest.mark.query_guard(detect_n_plus_one=True, n_plus_one_threshold=2)
def test_user_loop():
    # Executes SELECT * FROM auth_user WHERE id = ? twice
    for user_id in [10, 20]:
        User.objects.get(id=user_id)

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3. Using as a Context Manager (with query_guard(...))

You can also use query_guard directly inside Django views, Celery tasks, management commands, or standard unit tests:

from django_query_guard import query_guard, NPlusOneQueryError

def process_latest_orders():
    with query_guard(max_queries=5, detect_n_plus_one=True):
        orders = Order.objects.filter(status="pending").select_related("user")
        for order in orders:
            print(order.user.email)

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4. How to Fix Detected N+1 Queries in Django

When django-query-guard catches an N+1 query, fix it using Django's ORM optimization methods:

Fix 1: Use select_related for Foreign Keys (One-to-One / Many-to-One)

# ❌ Before (N+1 Queries)
books = Book.objects.all()
authors = [book.author.name for book in books]

# ✅ After (1 Query via JOIN)
books = Book.objects.select_related("author").all()
authors = [book.author.name for book in books]

Fix 2: Use prefetch_related for Reverse Foreign Keys / Many-to-Many

# ❌ Before (N+1 Queries)
authors = Author.objects.all()
books = [author.books.all() for author in authors]

# ✅ After (2 Queries Total)
authors = Author.objects.prefetch_related("books").all()
books = [author.books.all() for author in authors]

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🛠️ Custom Exceptions

django-query-guard provides explicit exceptions to catch in your application or test suites:

• QueryGuardError: Base class for all package exceptions.
• QueryCountExceededError: Raised when query count exceeds max_queries.
• NPlusOneQueryError: Raised when duplicate normalized SQL statements are executed.

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📄 License

This project is licensed under the MIT License.

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👤 Author & Maintainer

Atiqur Rahman
Software QA Engineer | SDET | Test Automation Architect | Microsoft Contributor | Open Source Contributor
📍 Dhaka, Bangladesh | ✉️ rahman.atiqur.pro@gmail.com | 🌐 LinkedIn | 🐙 GitHub Profile