django-check

Static N+1 query detection for Django, directly in VS Code.

This extension runs a bundled static analyzer to detect common N+1 query patterns before runtime. It analyzes Django ORM usage and reports missing select_related / prefetch_related calls as editor diagnostics.

No runtime hooks. No configuration. No external dependencies.

What it does

Detects N+1 query patterns statically
Shows diagnostics while you edit
Zero runtime overhead
No code instrumentation
Works alongside Pyright and other Python LSPs

What it detects

Related-field access inside QuerySet iteration without prefetching:

ForeignKey
OneToOne
ManyToMany
Reverse relations
Model inheritance

Example

users = User.objects.all()

for user in users:
    user.profile.bio  # N+1

Diagnostic:

[N+1] user.profile
Potential N+1 query: accessing `user.profile` inside loop

Fix:

users = User.objects.select_related("profile")

for user in users:
    user.profile.bio

The diagnostic is cleared once the relation is prefetched.

Installation

Install the extension from the VS Code Marketplace.

The analyzer binary is bundled with the extension. Nothing to install. Nothing to configure.

Usage

Open a Django project in VS Code.

The language server starts automatically when a project root is detected via:

manage.py
pyproject.toml
.git

Diagnostics appear as you edit Python files.

Limitations

This project is under active development.

Current limitations include:

Limited interprocedural analysis
Partial support for Prefetch objects
Limited understanding of:
- annotate
- aggregate
- complex custom managers
Incomplete handling of implicit chained prefetches, e.g.:

prefetch_related("chat__users__profile")

Expect false positives and false negatives.

Reference

Analyzer and language server source:

https://github.com/richardhapb/django-check

(The extension bundles the binary; the link is for reference only.)

License

MIT

Django-Check

richardhapb