NestJS Notification Architecture

Priority: P0 (CRITICAL)

Implement "Dual-Write" notification system: persist to Database (In-App) and send via FCM (Push).

Workflow: Send Notification

1. Save to database — Persist notification entity with type enum and metadata.
2. Check FCM token — Verify recipient valid fcmToken; skip push if missing.
3. Send push — Call FCM inside try/catch; never let FCM failure block request.
4. Serialize data — Convert Dates to ISO strings; keep FCM data payload flat (IDs only).

Dual-Write Service Example

See implementation examples

Structure

See implementation examples

Implementation Guidelines

• Use Dual-Write: Save to DB first, then attempt FCM. Catch FCM errors so they don't block logic.
• Define Granular Types: Use NotificationType Enum (e.g., APPOINTMENT_REMINDER) for frontend icon/color logic.
• Stringify Metadata: Store routing data (IDs) as JSON string in DB, but Map to string-only Key-Values for FCM data.
• Handle Tokens: Check for fcmToken existence before sending. Fail gracefully if missing.
• Serialize Dates: Convert Dates to ISO strings before sending to FCM.

Anti-Patterns

• No Generic Types: Avoid type: string. Always use Enum.
• No Blocking FCM: Never await FCM without try/catch. It shouldn't crash request.
• No Complex Data in Push: Keep FCM data payload flat and minimal (IDs only). Fetch details on open.

References

• Service Pattern (Dual-Write)
• Type Definitions