Rule reference

🌐 Tiếng Việt — queryset rules (DOL001–DOL007)

Django ORM Lens ships two rule surfaces:

1. Editor rules (DOL###) — 16 line-oriented static checks that run inside the VS Code extension on every .py file. Findings appear in the Problems panel under the source Django ORM Lens, link to these pages from the diagnostic code, and — where a fix is safe to express as a text edit — carry a QuickFix lightbulb. Detection is regex-based with bounded windows; no Python process is involved.
2. CLI / CI analyzers — AST-based checks in the Python package (pip install django-orm-lens) for terminals and pipelines: migration-risk, nplusone, blast-radius — which joins migration risks with the code that still references what they change — and drift, a makemigrations --check that needs no Django boot.

Severity and applicability

Severity mirrors VS Code's four diagnostic levels: error, warning, info, hint. Every rule has a default (listed below); override per rule in .vscode/settings.json via djangoOrmLens.rules — e.g. {"djangoOrmLens.rules": {"DOL013": "error", "DOL007": "off"}}.

Applicability follows Clippy's semantics. It is a property of each individual finding and gates whether an editor may apply the fix unattended:

Applicability	Meaning
safe	Semantically equivalent, always correct to apply. Eligible for auto-apply and "Fix All".
suggestion	Usually right but may need review — offered as a QuickFix, never included in "Fix All".
unsafe	Likely-correct but breaks in edge cases — surfaced as a diagnostic only, never auto-applied.

Editor rules

Code	Rule	Category	Default severity	Applicability
DOL001	Prefer .exists() over .count() > 0	queryset	info	safe
DOL002	Prefer not .exists() over .count() == 0	queryset	info	safe
DOL003	Prefer not .exists() over .first() is None	queryset	info	safe
DOL004	Prefer .exists() over .first() is not None	queryset	info	safe
DOL005	Consider Q(...) over .filter().exclude() chain	queryset	hint	suggestion
DOL006	Drop list() around a QuerySet in for-loop	queryset	info	safe
DOL007	Possible N+1: attribute access inside for-loop	queryset	warning	unsafe
DOL008	Field name in a lookup looks misspelled	correctness	warning	suggestion
DOL011	null=True on CharField/TextField	model	warning	suggestion
DOL012	Model without __str__ method	model	info	suggestion
DOL013	ForeignKey without on_delete	model	error	suggestion
DOL014	CharField without max_length	model	error	suggestion
DOL015	TextField with max_length has no DB effect	model	hint	suggestion
DOL021	datetime.now() should be timezone.now()	datetime	warning	suggestion
DOL022	datetime.utcnow() is deprecated	datetime	warning	suggestion
DOL031	render() with locals() as context	forms	warning	suggestion
DOL032	fields = '__all__' in Meta	forms	warning	unsafe

Suppressing findings inline

# django-orm-lens-disable-next-line DOL007        (next line; comma-separate for several codes)
qs.count() > 0  # django-orm-lens-disable-line DOL001
# django-orm-lens-disable DOL011                  (own line — disables for the rest of the file)

Ruff-style bulk selection is also available: djangoOrmLens.rulesSelect (e.g. ["DOL0"]) and djangoOrmLens.rulesIgnore (e.g. ["DOL03"]).

CLI / CI analyzers

These run from the Python CLI, not the editor. Both exit non-zero on findings (see each page for exact semantics) and emit --format sarif (SARIF 2.1.0 for GitHub Code Scanning) or --format github (workflow commands for zero-setup PR annotations).

• Migration risk rules — 16 rules over <app>/migrations/*.py flagging operations that are dangerous on production databases. Run with django-orm-lens migration-risk.
• Static N+1 detector — flags FK / O2O / M2M / reverse-manager access inside for-loops when the source queryset has no matching select_related / prefetch_related. Run with django-orm-lens nplusone.