core: fix: upsert each user when setting roles in bulk

[AntaresQAQ]

Summary

Fixes #1223.

The array branch of DomainModel.setUserRole currently uses updateMany with an $in filter and upsert: true. This does not create a record for each missing UID: partially matching batches leave missing users untouched, while entirely unmatched batches can create a document without a UID and trigger a duplicate-key error.

Replace this with a single bulkWrite containing an updateOne upsert for each { domainId, uid } pair.

• Return early for empty UID arrays to avoid an empty-batch error.
• Preserve existing cache invalidation and autojoin behavior.
• Leave the single-UID branch unchanged.
• Do not modify or remove existing malformed records.

This PR contains only the model fix; no test code or test data is included.

Validation

Verified with temporary regression tests against MongoDB 8.0:

• All target records missing, partially missing, and all existing.
• Repeated calls and empty UID arrays.
• autojoin enabled and disabled, including preservation of existing join status.
• Existing documents without a UID.
• set_users with join: true through the HTTP handler.

The original implementation failed six of the eight regression cases; the fixed implementation passed all eight.

Targeted ESLint and backend TypeScript checks with --skipLibCheck passed. Without --skipLibCheck, the type check is blocked by an existing third-party declaration error involving @types/koa and content-disposition.

Summary by CodeRabbit

• Bug Fixes
  • Improved role assignment for multiple users by applying updates individually and avoiding duplicate user IDs.
  • Refreshed affected users’ cached data after role changes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 4a0a1f81-9889-4be3-b742-d123651532d1

📥 Commits

Reviewing files that changed from the base of the PR and between b6b1b25 and 9f14c63.

📒 Files selected for processing: 1

• packages/hydrooj/src/model/domain.ts

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Walkthrough

For an empty UID array, DomainModel.setUserRole now returns undefined. For a nonempty array, it preserves the affected-user lookup and cache deletion, then uses bulkWrite to upsert one record per distinct UID instead of issuing a single upserting updateMany.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 9f14c

Bulk role assignment now creates or updates a record for each distinct target UID. No actionable merge risk was established in the inspected behavior.

Pre-merge checks: 5

Passed checks: 5 passed

Check name	Status	Explanation
Linked Issues check		The change addresses issue #1223. The array branch deduplicates UIDs and uses one bulkWrite updateOne upsert per { domainId, uid }. It returns for an empty array, preserves cache invalidation an…
Out of Scope Changes check		The change is limited to packages/hydrooj/src/model/domain.ts. The modified code directly fixes the bulk upsert behavior required by issue #1223. No unrelated implementation, test-data, or cleanup c…
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: creating or updating each user record during bulk role assignment.

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