Heldinhow/dotnet-mediatr

MediatR Pattern

Overview

MediatR is a mediator pattern implementation that enables decoupled request handling in .NET. This skill should be invoked when implementing CQRS, needing decoupled handlers, or requiring pipeline behaviors for cross-cutting concerns.

Core Principles

• Mediator Pattern: Decouple senders from receivers
• Request/Handler: Each request has one handler
• Pipeline Behaviors: Add cross-cutting concerns (logging, validation)
• Notification Patterns: Support for publish/subscribe

Preparation Checklist

• [ ] Install MediatR: dotnet add package MediatR
• [ ] Install DI extensions: dotnet add package MediatR.Extensions.Microsoft.DependencyInjection
• [ ] Plan request/command structure
• [ ] Configure in Program.cs

Step-by-Step Process

1. Install: Add MediatR packages
2. Define: Create request/command records
3. Implement: Build request handlers
4. Behaviors: Add pipeline behaviors
5. Register: Configure in DI
6. Use: Inject MediatR in controllers

Do's and Don'ts

• ✅ Do use for CQRS implementations
• ✅ Do add pipeline behaviors for logging, validation
• ✅ Do keep handlers focused and single-purpose
• ❌ Don't use for simple direct calls
• ❌ Don't skip pipeline behaviors when needed
• ❌ Don't over-abstract simple scenarios

Anti-Patterns

• Over-Abstraction: Using MediatR for everything
• Fat Handlers: Putting too much in handlers
• No Behaviors: Ignoring pipeline behaviors
• Tight Coupling: Not using interface abstraction