OnlineCourseSystem.Notifications

Enterprise-grade notifications microservice for the Codeway Online Courses Platform. Handles multi-channel delivery (in-app, email, push) with event-driven architecture, outbox pattern, and comprehensive user preference management.

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🎯 Overview

Centralized notification hub that orchestrates multi-channel communication across the Codeway platform. Supports REST APIs and event-driven integration via RabbitMQ.

Core Capabilities:

• Multi-channel delivery (In-app, Email, Push)
• User preference management per notification type
• Event-driven architecture (MassTransit + RabbitMQ)
• Outbox pattern for reliable delivery
• Scheduled notifications
• Direct messaging between users
• Device management for push notifications

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🏗️ Architecture

External Services → REST API / RabbitMQ Events
         ↓
Controllers → CQRS (MediatR) → Services → Repositories → SQL Server
         ↓
Background Workers (EmailOutbox, PushOutbox, Scheduled)

Data Flow:

1. Request/Event → Validation → User Verification
2. sp_CreateNotification (stored procedure) creates notification + outbox items atomically
3. Background workers process outbox items asynchronously
4. Delivery tracking across all channels

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🛠️ Tech Stack

• .NET 8.0 + ASP.NET Core Web API
• EF Core 8.0 + SQL Server (stored procedures with TVPs)
• MassTransit 8.2 + RabbitMQ
• MediatR 14.0 (CQRS)
• FluentValidation 12.1
• Firebase Admin SDK (FCM push notifications)

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🚀 Quick Start

Prerequisites

• .NET 8.0 SDK
• SQL Server 2022+
• RabbitMQ (for events)
• Firebase project (for push)

Setup

1. Restore & Configure

   dotnet restore OnlineCourseSystem.sln

   Update appsettings.json with connection strings and credentials.

2. Database Setup

   dotnet ef database update --project OnlineCourseSystem.Notifications

   Execute Infrastructure/Database/SP_CreateNotification.sql

3. Run

   dotnet run --project OnlineCourseSystem.Notifications

   Swagger UI: https://localhost:5001/swagger

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⚙️ Configuration

Setting	Description
ConnectionStrings:DefaultConnection	SQL Server connection string
RabbitMq:Host/Username/Password	RabbitMQ connection
EmailSettings:*	SMTP configuration
Firebase:CredentialsPath	Firebase service account JSON path
WorkerSettings:*	Batch sizes and polling intervals

Override via environment variables: ConnectionStrings__DefaultConnection=...

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📚 API Examples

Create Notification

POST /api/notifications
{
  "notificationType": "Course",
  "title": "New lesson available!",
  "content": "Lesson 5 is now available.",
  "courseId": "5f2c8c2c-18d8-46b0-b4e9-f0e4dc8e6a61",
  "userIds": ["c8c49232-4c8a-4f8c-8de1-4a70c7ad1140"]
}

Get User Notifications

GET /api/notifications?userId={userId}&isRead=false&pageNumber=1&pageSize=20

Update Preferences

POST /api/notificationpreferences/{userId}
{
  "notificationType": "Reminder",
  "email": true,
  "push": false,
  "inApp": true
}

Schedule Notification

POST /api/schedulednotifications
{
  "notificationType": "Reminder",
  "title": "Assignment due soon",
  "content": "Your assignment is due in 2 days",
  "userIds": ["user-id-1"],
  "scheduledFor": "2024-12-25T10:00:00Z"
}

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🔄 Background Workers

• EmailOutboxWorker: Processes pending emails (batch size: 10, interval: 30s)
• PushOutboxWorker: Sends push notifications via FCM (batch size: 10, interval: 30s)
• ScheduledNotificationWorker: Processes scheduled notifications (batch size: 10, interval: 60s)

All workers include retry logic with exponential backoff.

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📡 Event-Driven Integration

Consumes events via RabbitMQ:

• NotificationRequestedEvent: Creates notifications for specified users
• UserEnrolledEvent: Auto-creates welcome notifications
• PaymentSucceededEvent: Creates payment confirmation notifications

Events are automatically consumed via MassTransit consumers registered in Program.cs.

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🗄️ Database

Core Tables: Notifications, UserNotifications, NotificationPreferences, UserReferences, UserNotificationDeliveries

Outbox Tables: EmailOutbox, PushOutbox, ScheduledNotifications

Stored Procedures:

• sp_CreateNotification: Atomic notification creation with TVP
• sp_GetUserNotifications: Paginated user notification retrieval

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✅ Validation & Error Handling

• FluentValidation: Automatic validation via MediatR pipeline behaviors
• ExceptionMiddleware: Global exception handler with structured logging
• Custom Exceptions: BadRequestException, NotFoundException
• Standardized Responses: Via GlobalResponse.Shared

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🧪 Development

# Run tests
dotnet test OnlineCourseSystem.sln

# Format code
dotnet format OnlineCourseSystem.Notifications

# Create migration
dotnet ef migrations add <Name> --project OnlineCourseSystem.Notifications

# Apply migration
dotnet ef database update --project OnlineCourseSystem.Notifications

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🚢 Deployment

dotnet publish OnlineCourseSystem.Notifications -c Release -o ./publish/notifications

Checklist:

• Production connection strings configured
• RabbitMQ cluster setup (if using events)
• Firebase credentials configured
• SMTP credentials configured
• Database migrations applied
• Stored procedures executed
• Logging/monitoring configured
• Worker settings tuned

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📁 Project Structure

OnlineCourseSystem.Notifications/
├── Controllers/          # REST endpoints
├── Consumers/            # MassTransit event consumers
├── Features/            # CQRS feature modules (Commands/Queries/Handlers)
├── Infrastructure/
│   ├── Database/        # Stored procedures
│   ├── Repositories/     # Data access (Unit of Work)
│   └── Services/         # Domain services
├── Workers/              # Background services
├── Models/               # Entities, DbContext, Enums
└── Validators/           # FluentValidation rules

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🤝 Contributing

1. Fork & create feature branch
2. Follow coding standards (nullable ref types, async/await, logging)
3. Add tests for new functionality
4. Run dotnet format and dotnet test
5. Submit PR with detailed description

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Built with ❤️ for the Codeway Online Courses Platform