Heldinhow 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
- Install: Add MediatR packages
- Define: Create request/command records
- Implement: Build request handlers
- Behaviors: Add pipeline behaviors
- Register: Configure in DI
- 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