Add username filter to ReadEnvelopeReceiverQuery handler

Extended ReadEnvelopeReceiverQuery to support optional username-based filtering. Refactored the handler to apply this filter, updated repository access for consistency, and improved code clarity and null-safety. Cleaned up comments and formatting.

EnvelopeGenerator.Application/EnvelopeReceivers/Queries/ReadEnvelopeReceiverQuery.cs

@@ -1,4 +1,4 @@
-using AutoMapper;
+using AutoMapper;
 using DigitalData.Core.Abstraction.Application.Repository;
 using DigitalData.Core.Exceptions;
 using EnvelopeGenerator.Application.Envelopes.Queries;
@@ -47,7 +47,13 @@ namespace EnvelopeGenerator.Application.EnvelopeReceivers.Queries;
 /// Die Antwort enthält Details wie den Include, die Zuordnung zwischen Umschlag und Empfänger 
 /// sowie zusätzliche Metadaten.
 /// </remarks>
-public record ReadEnvelopeReceiverQuery : EnvelopeReceiverQueryBase<ReadEnvelopeQuery, ReadReceiverQuery>, IRequest<IEnumerable<EnvelopeReceiverDto>>;
+public record ReadEnvelopeReceiverQuery : EnvelopeReceiverQueryBase<ReadEnvelopeQuery, ReadReceiverQuery>, IRequest<IEnumerable<EnvelopeReceiverDto>>
+{
+    /// <summary>
+    /// Optionaler Benutzernamefilter, um Ergebnisse auf Umschläge eines bestimmten Besitzers einzuschränken.
+    /// </summary>
+    public string? Username { get; init; }
+}
 
 /// <summary>
 /// 
@@ -82,24 +88,15 @@ public static class Extensions
         q.Receiver.Signature = signature;
         return mediator.Send(q, cancel).Then(envRcvs => envRcvs.FirstOrDefault());
     }
-}
-
     /// <summary>
-/// 
+    /// Verarbeitet <see cref="ReadEnvelopeReceiverQuery"/> und liefert passende <see cref="EnvelopeReceiverDto"/>-Ergebnisse.
     /// </summary>
     public class ReadEnvelopeReceiverQueryHandler : IRequestHandler<ReadEnvelopeReceiverQuery, IEnumerable<EnvelopeReceiverDto>>
     {
         private readonly IRepository<EnvelopeReceiver> _repo;
-
         private readonly IRepository<Receiver> _rcvRepo;
-
         private readonly IMapper _mapper;
 
-    /// <summary>
-    /// 
-    /// </summary>
-    /// <param name="envelopeReceiver"></param>
-    /// <param name="mapper"></param>
         public ReadEnvelopeReceiverQueryHandler(IRepository<EnvelopeReceiver> envelopeReceiver, IRepository<Receiver> rcvRepo, IMapper mapper)
         {
             _repo = envelopeReceiver;
@@ -116,7 +113,10 @@ public class ReadEnvelopeReceiverQueryHandler : IRequestHandler<ReadEnvelopeRece
         /// <exception cref="BadRequestException"></exception>
         public async Task<IEnumerable<EnvelopeReceiverDto>> Handle(ReadEnvelopeReceiverQuery request, CancellationToken cancel)
         {
-        var q = _repo.ReadOnly().Where(request, notnull: false);
+            var q = _repo.Query.Where(request, notnull: false);
+
+            if (request.Username is string username)
+                q = q.Where(er => er.Envelope!.User.Username == username);
 
             if (request.Envelope.Status is not null)
             {
@@ -141,14 +141,15 @@ public class ReadEnvelopeReceiverQueryHandler : IRequestHandler<ReadEnvelopeRece
                             .Include(er => er.Receiver)
                             .ToListAsync(cancel);
 
-        if (request.Receiver.HasAnyCriteria && envRcvs.Any())
+            if (request.Receiver.HasAnyCriteria && envRcvs.Count != 0)
             {
-            var receiver = await _rcvRepo.ReadOnly().Where(request.Receiver).FirstAsync(cancel);
+                var receiver = await _rcvRepo.Query.Where(request.Receiver).FirstAsync(cancel);
 
                 foreach (var envRcv in envRcvs)
-                envRcv.Envelope?.Documents?.First().Elements.RemoveAll(s => s.ReceiverId != receiver.Id);
+                    envRcv.Envelope?.Documents?.FirstOrDefault()?.Elements?.RemoveAll(s => s.ReceiverId != receiver.Id);
             }
 
             return _mapper.Map<List<EnvelopeReceiverDto>>(envRcvs);
         }
     }
+}