---
issue: 100
title: "Backend: updatePurchaseRequest does findById then findByIdAndUpdate — non-atomic race"
severity: medium
domain: Marketplace
labels: [bug, backend, concurrency]
status: open
created: 2026-05-30
source: Full Codebase Audit 2026-05-30
---

# Backend: updatePurchaseRequest does findById then findByIdAndUpdate — non-atomic race

**Severity:** medium
**Domain:** Marketplace
**Labels:** bug, backend, concurrency

## Description

`PurchaseRequestService.ts:413` reads the document first (`findById`) to check allowed status transitions, then writes it (`findByIdAndUpdate`). Between the read and the write, another request can change the status, defeating the transition guard.

## Options

1. Use `findOneAndUpdate` with `status:{$in:allowedCurrentStatuses}` condition — atomic.
2. Keep two queries but wrap in a transaction.
3. Leave as-is.

## Recommendation

Use a single conditional `findOneAndUpdate` to make the transition atomic and halve round-trips.

## Affected Files

- `backend/src/services/marketplace/PurchaseRequestService.ts:413`

## References

- [Full Codebase Audit 2026-05-30](../09%20-%20Audits/Full%20Codebase%20Audit%20-%202026-05-30.md) — DEC-46