NestJS Notification Architecture

Priority: P0 (Standard)

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

Structure

src/modules/notification/
├── notification.service.ts   # Logic: DB Save + FCM Send
├── entities/
│   └── notification.entity.ts # DB Schema + NotificationType Enum
└── types/
    └── notification.types.ts  # Interfaces for Payloads/Metadata

Implementation Guidelines

• Use Dual-Write: Save to DB first, then attempt FCM. Catch FCM errors so they don't block the 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 the Enum.
• No Blocking FCM: Never await FCM without a try/catch. It shouldn't crash the request.
• No Complex Data in Push: Keep FCM data payload flat and minimal (IDs only). Fetch details on open.

Reference & Examples

• Service Pattern (Dual-Write): references/service.md
• Type Definitions: references/types.md