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fix: Reduce likelihood of race condition in Matching #1157

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Nov 6, 2024
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fix: Reduce likelihood of race condition in Matching #1157

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9 changes: 7 additions & 2 deletions common/match/create.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -16,11 +16,16 @@ const logger = getLogger('Match');
export async function createMatch(pupil: Pupil, student: Student, pool: ConcreteMatchPool) {
const uuid = generateUUID();

if (pupil.openMatchRequestCount < 1) {
// Refetch match request count to reduce the likelihood of race conditions
// (does not prevent it though, we would actually need a SELECT FOR UPDATE)
const freshPupil = await prisma.pupil.findUniqueOrThrow({ where: { id: pupil.id }, select: { openMatchRequestCount: true } });
const freshStudent = await prisma.student.findUniqueOrThrow({ where: { id: student.id }, select: { openMatchRequestCount: true } });

if (freshPupil.openMatchRequestCount < 1) {
throw new PrerequisiteError(`Cannot create Match for Pupil without open match requests`);
}

if (student.openMatchRequestCount < 1) {
if (freshStudent.openMatchRequestCount < 1) {
throw new PrerequisiteError(`Cannot create Match for Student without open match request count`);
}

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