Context

MongoDB provides $setWindowFields for performing window-based calculations like running totals, rankings, and moving averages.

Definition of done

• Implement support for translating Window() ORM expressions into $setWindowFields.

• Support key operators ($sum, $avg, $rank, $denseRank, etc.).

• Add functional tests or check Django's test suite (e.g., running total, per-category rank)

Pitfalls

• $setWindowFields requires sorted input (sortBy); ordering must be validated.

• Must maintain consistency with Django’s SQL Window expression semantics.