first commit

MyNewProjectName.Application/Behaviors/ValidationBehavior.cs

@@ -0,0 +1,47 @@
+using FluentValidation;
+using MediatR;
+
+namespace MyNewProjectName.Application.Behaviors;
+
+/// <summary>
+/// Validation behavior for MediatR pipeline
+/// </summary>
+public class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : notnull
+{
+    private readonly IEnumerable<IValidator<TRequest>> _validators;
+
+    public ValidationBehavior(IEnumerable<IValidator<TRequest>> validators)
+    {
+        _validators = validators;
+    }
+
+    public async Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken cancellationToken)
+    {
+        if (!_validators.Any())
+        {
+            return await next();
+        }
+
+        var context = new ValidationContext<TRequest>(request);
+
+        var validationResults = await Task.WhenAll(
+            _validators.Select(v => v.ValidateAsync(context, cancellationToken)));
+
+        var failures = validationResults
+            .Where(r => r.Errors.Any())
+            .SelectMany(r => r.Errors)
+            .ToList();
+
+        if (failures.Any())
+        {
+            var errors = failures
+                .GroupBy(e => e.PropertyName, e => e.ErrorMessage)
+                .ToDictionary(g => g.Key, g => g.ToArray());
+
+            throw new MyNewProjectName.Domain.Exceptions.ValidationException(errors);
+        }
+
+        return await next();
+    }
+}