Fermat.Cqrs.Behaviors 0.0.1

Fermat.Cqrs.Behaviors

A comprehensive .NET library providing cross-cutting concerns as MediatR pipeline behaviors for CQRS applications. This library offers ready-to-use behaviors for authentication, authorization, logging, performance monitoring, retry mechanisms, transaction management, and validation.

🚀 Features

🔐 Authentication & Authorization

• AuthorizationBehavior: Enforces authentication and role-based authorization
• Supports multiple required roles per request
• Automatic user authentication verification
• Role-based access control with customizable role requirements

📝 Logging

• LoggingBehavior: Comprehensive request/response logging
• Request payload logging with structured data
• Response logging with execution time tracking
• Error logging with detailed exception information
• Performance metrics included in logs

⚡ Performance Monitoring

• PerformanceBehavior: Monitors request execution time
• Configurable performance thresholds (default: 500ms)
• Warning logs for long-running requests
• Request payload logging for performance analysis

🔄 Retry Mechanism

• RetryBehavior: Automatic retry for transient failures
• Configurable retry count and delay
• Smart transient exception detection
• Exponential backoff support via Polly
• Detailed retry logging

💾 Transaction Management

• TransactionScopeBehavior: Automatic transaction scope management
• Async transaction support
• Automatic rollback on exceptions
• Proper resource disposal

✅ Validation

• ValidationBehavior: FluentValidation integration
• Automatic request validation
• Structured validation error responses
• Support for multiple validators per request

📦 Installation

  dotnet add package Fermat.Cqrs.Behaviors

🛠️ Dependencies

• .NET 8.0
• MediatR (13.0.0) - For pipeline behavior support
• FluentValidation (12.0.0) - For request validation
• Polly (8.6.2) - For retry policies
• Microsoft.AspNetCore.Http.Abstractions (2.3.0) - For HTTP context access
• Fermat.Domain.Exceptions (0.0.1) - For custom exception types

🔧 Configuration

Register Behaviors in DI Container

// Program.cs or Startup.cs
services.AddMediatR(cfg => {
    cfg.RegisterServicesFromAssembly(typeof(YourAssembly).Assembly);
    
    // Register pipeline behaviors in execution order
    cfg.AddBehavior(typeof(ValidationBehavior<,>));
    cfg.AddBehavior(typeof(LoggingBehavior<,>));
    cfg.AddBehavior(typeof(PerformanceBehavior<,>));
    cfg.AddBehavior(typeof(RetryBehavior<,>));
    cfg.AddBehavior(typeof(AuthorizationBehavior<,>));
    cfg.AddBehavior(typeof(TransactionScopeBehavior<,>));
});

// Required services
services.AddHttpContextAccessor();
services.AddLogging();

📖 Usage Examples

1. Authentication & Authorization

public class CreateUserCommand : IRequest<CreateUserResponse>, IAuthorizeBehavior
{
    public IReadOnlyCollection<string> RequiredRoles => new[] { "Admin", "UserManager" };
    
    public string Username { get; set; }
    public string Email { get; set; }
}

public class CreateUserCommandHandler : IRequestHandler<CreateUserCommand, CreateUserResponse>
{
    public async Task<CreateUserResponse> Handle(CreateUserCommand request, CancellationToken cancellationToken)
    {
        // Your business logic here
        return new CreateUserResponse { UserId = Guid.NewGuid() };
    }
}

2. Logging

public class GetUserQuery : IRequest<GetUserResponse>, ILoggingBehavior
{
    public Guid UserId { get; set; }
}

3. Performance Monitoring

public class ComplexCalculationCommand : IRequest<CalculationResult>, IPerformanceBehavior
{
    public int ThresholdMilliseconds => 1000; // Custom threshold
    
    public decimal[] Numbers { get; set; }
}

4. Retry Mechanism

public class ExternalApiCallCommand : IRequest<ApiResponse>, IRetryBehavior
{
    public int RetryCount => 5; // Custom retry count
    public int RetryDelayMilliseconds => 1000; // Custom delay
    
    public string ApiEndpoint { get; set; }
}

5. Transaction Management

public class TransferMoneyCommand : IRequest<TransferResult>, ITransactionBehavior
{
    public Guid FromAccountId { get; set; }
    public Guid ToAccountId { get; set; }
    public decimal Amount { get; set; }
}

6. Validation

public class CreateProductCommand : IRequest<CreateProductResponse>
{
    public string Name { get; set; }
    public decimal Price { get; set; }
    public int StockQuantity { get; set; }
}

public class CreateProductCommandValidator : AbstractValidator<CreateProductCommand>
{
    public CreateProductCommandValidator()
    {
        RuleFor(x => x.Name).NotEmpty().MaximumLength(100);
        RuleFor(x => x.Price).GreaterThan(0);
        RuleFor(x => x.StockQuantity).GreaterThanOrEqualTo(0);
    }
}

🔄 Behavior Execution Order

The recommended execution order for pipeline behaviors:

1. ValidationBehavior - Validate request first
2. LoggingBehavior - Log incoming request
3. PerformanceBehavior - Start performance monitoring
4. RetryBehavior - Handle transient failures
5. AuthorizationBehavior - Check authentication/authorization
6. TransactionScopeBehavior - Manage transactions
7. Your Handler - Execute business logic
8. Behaviors in reverse order - Complete monitoring, logging, etc.

🎯 Best Practices

1. Interface Implementation

• Implement behavior interfaces only when needed
• Use default values when possible to reduce boilerplate
• Combine multiple behaviors for comprehensive request handling

2. Performance Considerations

• Set appropriate performance thresholds based on your application needs
• Monitor and adjust retry policies based on failure patterns
• Use logging judiciously to avoid performance impact

3. Security

• Always implement authorization for sensitive operations
• Use role-based access control effectively
• Validate all user inputs

4. Error Handling

• Leverage retry behavior for transient failures
• Use transaction behavior for data consistency
• Implement proper validation for data integrity

🐛 Troubleshooting

Common Issues

1. Behaviors not executing: Ensure behaviors are registered in the correct order
2. Validation not working: Verify FluentValidation validators are registered in DI
3. Authorization failing: Check if IHttpContextAccessor is registered
4. Retry not working: Verify exception types are considered transient