From 6c54473d5aa6a73dd9d7d1e26c8e105a9a252315 Mon Sep 17 00:00:00 2001
From: TekH <h.tek@digitaldata.works>
Date: Wed, 8 Apr 2026 13:44:19 +0200
Subject: [PATCH] Refactor MediatorExtensions for flexible exception handling

Generalize null/empty response handling with SendOrThrowAsync<TResponse, TException>, allowing custom exceptions via a factory delegate. SendOrNotFoundAsync now wraps this method for NotFoundException. Improves type safety, flexibility, and XML docs; avoids treating strings as collections.
---
 .../Common/Extensions/MediatorExtensions.cs   | 46 +++++++++++++------
 1 file changed, 31 insertions(+), 15 deletions(-)

diff --git a/EnvelopeGenerator.Application/Common/Extensions/MediatorExtensions.cs b/EnvelopeGenerator.Application/Common/Extensions/MediatorExtensions.cs
index ea971903..b0a09668 100644
--- a/EnvelopeGenerator.Application/Common/Extensions/MediatorExtensions.cs
+++ b/EnvelopeGenerator.Application/Common/Extensions/MediatorExtensions.cs
@@ -9,6 +9,32 @@ namespace EnvelopeGenerator.Application.Common.Extensions;
 /// </summary>
 public static class MediatorExtensions
 {
+    /// <summary>
+    /// Sends a request via MediatR and throws a custom exception produced by <paramref name="exceptionFactory"/>
+    /// when the response is <c>null</c> or an empty collection.
+    /// </summary>
+    /// <typeparam name="TResponse">The expected response type.</typeparam>
+    /// <typeparam name="TException">The exception type to throw.</typeparam>
+    /// <param name="mediator">The mediator instance.</param>
+    /// <param name="request">The MediatR request whose response may be <c>null</c>.</param>
+    /// <param name="exceptionFactory">A factory that creates the exception to throw when the response is absent.</param>
+    /// <param name="cancel">Cancellation token.</param>
+    /// <returns>A guaranteed non-null <typeparamref name="TResponse"/>.</returns>
+    /// <exception cref="Exception">The exception produced by <paramref name="exceptionFactory"/>.</exception>
+    public static async Task<TResponse> SendOrThrowAsync<TResponse, TException>(this IMediator mediator, IRequest<TResponse?> request, Func<TException> exceptionFactory, CancellationToken cancel = default)
+        where TException : Exception
+    {
+        if (await mediator.Send(request, cancel) is TResponse res)
+        {
+            if (res is not string && res is IEnumerable enumerable && !enumerable.Cast<object>().Any())
+                throw exceptionFactory();
+
+            return res;
+        }
+
+        throw exceptionFactory();
+    }
+
     /// <summary>
     /// Sends a request via MediatR and throws <see cref="NotFoundException"/> when the response is <c>null</c> or an empty collection.
     /// </summary>
@@ -16,23 +42,13 @@ public static class MediatorExtensions
     /// <param name="mediator">The mediator instance.</param>
     /// <param name="request">The MediatR request whose response may be <c>null</c>.</param>
     /// <param name="exceptionMessage">Optional message for the <see cref="NotFoundException"/>.</param>
-    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <param name="cancel">Cancellation token.</param>
     /// <returns>A guaranteed non-null <typeparamref name="TResponse"/>.</returns>
     /// <exception cref="NotFoundException">Thrown when the response is <c>null</c> or an empty collection.</exception>
-    public static async Task<TResponse> SendOrNotFoundAsync<TResponse>(this IMediator mediator, IRequest<TResponse?> request, string? exceptionMessage, CancellationToken cancellationToken = default)
-    {
-        if(await mediator.Send(request, cancellationToken) is TResponse res)
-        {
-            if(res is IEnumerable enumerable && !enumerable.Cast<object>().Any())
-                throw new NotFoundException(exceptionMessage);
-
-            return res;
-        }
-
-        throw new NotFoundException(exceptionMessage);
-    }
+    public static async Task<TResponse> SendOrNotFoundAsync<TResponse>(this IMediator mediator, IRequest<TResponse?> request, string? exceptionMessage, CancellationToken cancel = default)
+        => await mediator.SendOrThrowAsync(request, () => new NotFoundException(exceptionMessage ?? $"The requested resource of type {typeof(TResponse).Name} was not found."), cancel);
 
     /// <inheritdoc cref="SendOrNotFoundAsync{TResponse}(IMediator, IRequest{TResponse}, string, CancellationToken)"/>
-    public static async Task<TResponse> SendOrNotFoundAsync<TResponse>(this IMediator mediator, IRequest<TResponse?> request, CancellationToken cancellationToken = default)
-        => await mediator.SendOrNotFoundAsync(request, null, cancellationToken);
+    public static async Task<TResponse> SendOrNotFoundAsync<TResponse>(this IMediator mediator, IRequest<TResponse?> request, CancellationToken cancel = default)
+        => await mediator.SendOrNotFoundAsync(request, null, cancel);
 }
\ No newline at end of file