Refaktorisierung von HomeController, um die Verwendung von ThenAsync zu integrieren und Codelesbarkeit zu verbessern.

EnvelopeGenerator.Application/DTOs/EnvelopeReceiverDto.cs

@@ -12,6 +12,6 @@ namespace EnvelopeGenerator.Application.DTOs
         string? PrivateMessage,
         DateTime AddedWhen,
         DateTime? ChangedWhen,
-        Envelope? Envelope,
+        EnvelopeDto? Envelope,
-        Receiver? Receiver);
+        ReceiverDto? Receiver);
 }

EnvelopeGenerator.Application/Services/EnvelopeReceiverService.cs

@@ -99,7 +99,7 @@ namespace EnvelopeGenerator.Application.Services
             (string? uuid, string? signature) = envelopeReceiverId.DecodeEnvelopeReceiverId();
 
             if (uuid is null || signature is null)
-                return Result.Fail<bool>();
+                return Result.Fail<bool>().Notice(LogLevel.Warning, EnvelopeFlag.NonDecodableEnvelopeReceiverId, "In IsExisting(string envelopeReceiverId)");
 
             int count = await _repository.CountAsync(uuid:uuid, signature:signature);
             return Result.Success(count > 0);

EnvelopeGenerator.Web/Controllers/ControllerBaseExtensions.cs

@@ -40,6 +40,7 @@ namespace EnvelopeGenerator.Web.Controllers
             return null;
         }
 
+        //TODO: integrate localizer for ready-to-use views
         public static ViewResult ViewError(this Controller controller, ErrorViewModel errorViewModel) => controller.View("_Error", errorViewModel);
 
         public static ViewResult ViewError404(this Controller controller) => controller.ViewError(new ErrorViewModel()
@@ -50,6 +51,13 @@ namespace EnvelopeGenerator.Web.Controllers
         });
 
         public static ViewResult ViewEnvelopeNotFound(this Controller controller) => controller.ViewError(new ErrorViewModel()
+        {
+            Title = "404",
+            Subtitle = "Document not found",
+            Body = "Wenn Sie diese URL in Ihrer E-Mail erhalten haben, wenden Sie sich bitte an das IT-Team."
+        });
+
+        public static ViewResult ViewDocumentNotFound(this Controller controller) => controller.ViewError(new ErrorViewModel()
         {
             Title = "404",
             Subtitle = "Umschlag nicht gefunden",

EnvelopeGenerator.Web/Controllers/HomeController.cs

@@ -12,6 +12,7 @@ using EnvelopeGenerator.Application;
 using Microsoft.Extensions.Localization;
 using DigitalData.Core.DTO;
 using EnvelopeGenerator.Application.Resources;
+using EnvelopeGenerator.Application.DTOs;
 
 namespace EnvelopeGenerator.Web.Controllers
 {
@@ -38,43 +39,34 @@ namespace EnvelopeGenerator.Web.Controllers
             ViewData["EnvelopeKey"] = envelopeReceiverId;
             try
             {
-                var erResult = await _envRcvService.ReadByEnvelopeReceiverIdAsync(envelopeReceiverId: envelopeReceiverId);
+                return await _envRcvService.ReadByEnvelopeReceiverIdAsync(envelopeReceiverId: envelopeReceiverId).ThenAsync<EnvelopeReceiverDto, IActionResult>(
-                var er = erResult.Data;
+                    SuccessAsync: async er =>
-                var receiver = er?.Receiver;
-                var envelope = er?.Envelope;
-                var mailAddress = receiver?.EmailAddress;
-
-                if (erResult is null)
-                {
-                    _logger.LogError(_localizer[MessageKey.ServiceOutputNullError.ToString()]);
-                    return this.ViewEnvelopeNotFound();
-                }
-                else if (erResult.IsSuccess && mailAddress is not null && (envelope?.UseAccessCode ?? false))
                     {
                         EnvelopeResponse response = await envelopeOldService.LoadEnvelope(envelopeReceiverId);
 
                         bool accessCodeAlreadyRequested = database.Models.receiverModel.AccessCodeAlreadyRequested(response.Receiver.Email, response.Envelope.Id);
-                    accessCodeAlreadyRequested = await _historyService.AccessCodeAlreadyRequested(envelopeId: envelope.Id, userReference: mailAddress);
+
+                        accessCodeAlreadyRequested = await _historyService.AccessCodeAlreadyRequested(envelopeId: er.Envelope!.Id, userReference: er.Receiver!.EmailAddress);
                         if (!accessCodeAlreadyRequested)
                         {
                             // Send email with password
                             bool actionResult = database.Services.actionService.RequestAccessCode(response.Envelope, response.Receiver);
                             bool result = database.Services.emailService.SendDocumentAccessCodeReceivedEmail(response.Envelope, response.Receiver);
                         }
-                }
+
-                else
+                        return Redirect($"{envelopeReceiverId}/Locked");
+                    },
+                    Fail: (messages, notices) =>
                     {
-                    _logger.LogNotice(erResult);
+                        _logger.LogNotice(notices);
                         return this.ViewEnvelopeNotFound();
-                }
+                    });
             }
             catch(Exception ex)
             {
-                _logger.LogEnvelopeError(envelopeEeceiverId: envelopeReceiverId, exception:ex, message: _localizer[MessageKey.UnexpectedError.ToString()]);
+                _logger.LogEnvelopeError(envelopeEeceiverId: envelopeReceiverId, exception:ex, message: _localizer[MessageKey.UnexpectedError]);
                 return this.ViewInnerServiceError();
             }
-
-            return Redirect($"{envelopeReceiverId}/Locked");
         }
 
         [HttpGet("EnvelopeKey/{envelopeReceiverId}/Locked")]
@@ -82,13 +74,13 @@ namespace EnvelopeGenerator.Web.Controllers
         {
             try
             {
-                var result = await _envRcvService.IsExisting(envelopeReceiverId: envelopeReceiverId);
+                return await _envRcvService.IsExisting(envelopeReceiverId: envelopeReceiverId).ThenAsync(
-                bool isExisting = result.Data;
+                    Success: isExisting => isExisting ? View().WithData("EnvelopeKey", envelopeReceiverId) : this.ViewEnvelopeNotFound(),
-
+                    Fail: IActionResult (messages,notices) =>
-                if (result.HasFlag(EnvelopeFlag.NonDecodableEnvelopeReceiverId) || !isExisting)
+                    {
+                        _logger.LogNotice(notices);
                         return this.ViewEnvelopeNotFound();
-
+                    });
-                return View().WithData("EnvelopeKey", envelopeReceiverId);
             }
             catch(Exception ex)
             {
@@ -107,38 +99,30 @@ namespace EnvelopeGenerator.Web.Controllers
                 if(uuid is null || signature is null)
                 {
                     _logger.LogEnvelopeError(uuid: uuid, signature: signature, message: _localizer[MessageKey.WrongEnvelopeReceiverId.ToString()]);
-                    return BadRequest(_localizer[MessageKey.WrongEnvelopeReceiverId.ToString()]);
+                    return BadRequest(_localizer[MessageKey.WrongEnvelopeReceiverId]);
                 }
 
                 _logger.LogInformation($"Envelope UUID: [{uuid}]\nReceiver Signature: [{signature}]");
 
-                var verification = await _envRcvService.VerifyAccessCodeAsync(uuid: uuid, signature: signature, accessCode: access_code);
+                return await _envRcvService.VerifyAccessCodeAsync(uuid: uuid, signature: signature, accessCode: access_code).ThenAsync(
-                var isVerified = verification.Data;
+                    SuccessAsync: async isVerified =>
-
+                    {
                         EnvelopeResponse response = await envelopeOldService.LoadEnvelope(envelopeReceiverId);
-
+                        if (isVerified)
-                if (!verification.IsSuccess)
-                {
-                    _logger.LogNotice(verification);
-
-                    if (verification.HasFlag(Flag.SecurityBreach))
-                        return Forbid();
-
-                    return StatusCode(StatusCodes.Status500InternalServerError, string.Join(". ", verification.Messages).Append('.'));
-                }
-                else if (isVerified)
                         {
+                            //todo: write using crud-service (mostlikely history-service) to make it async
                             if (envelopeOldService.ReceiverAlreadySigned(response.Envelope, response.Receiver.Id))
                             {
                                 return View("EnvelopeSigned");
                             }
 
-                    var envelope = await _envelopeService.ReadByUuidAsync(uuid: uuid, signature: signature, withAll: true);
-
                             database.Services.actionService.EnterCorrectAccessCode(response.Envelope, response.Receiver);   //for history
                             ViewData["EnvelopeKey"] = envelopeReceiverId;
                             ViewData["EnvelopeResponse"] = response;
 
+                            return await _envRcvService.ReadByUuidSignatureAsync(uuid: uuid, signature: signature).ThenAsync<EnvelopeReceiverDto, IActionResult>(
+                                    SuccessAsync: async er =>
+                                    {
                                         if (response.Envelope.Documents.Count() > 0)
                                         {
                                             var document = await envelopeOldService.GetDocument(response.Envelope.Documents[0].Id, envelopeReceiverId);
@@ -146,38 +130,46 @@ namespace EnvelopeGenerator.Web.Controllers
                                             ViewData["DocumentBytes"] = bytes;
                                         }
                                         else
-                        ViewData["DocumentBytes"] = null;
-
-                    var claims = new List<Claim>
                                         {
-                        new Claim(ClaimTypes.NameIdentifier, uuid),
+                                            return this.ViewDocumentNotFound();
-                        new Claim(ClaimTypes.Hash, signature),
+                                        }
-                    };
+
+                                        var claims = new List<Claim> { new(ClaimTypes.NameIdentifier, uuid), new(ClaimTypes.Hash, signature) };
 
                                         var claimsIdentity = new ClaimsIdentity(claims, CookieAuthenticationDefaults.AuthenticationScheme);
-                    var authProperties = new AuthenticationProperties
+                                        var authProperties = new AuthenticationProperties { };
-                    {
-                    };
 
                                         await HttpContext.SignInAsync(
                                             CookieAuthenticationDefaults.AuthenticationScheme,
                                             new ClaimsPrincipal(claimsIdentity),
                                             authProperties);
 
-                    return View("ShowEnvelope", envelope);
+                                        return View("ShowEnvelope", er);
+                                    },
+                                    Fail: (messages, notices) =>
+                                    {
+                                        _logger.LogNotice(notices);
+                                        return this.ViewEnvelopeNotFound();
+                                    }
+                                );
                         }
                         else
                         {
                             database.Services.actionService.EnterIncorrectAccessCode(response.Envelope, response.Receiver); //for history
-                    _logger.LogWarning(string.Join("\n", verification.Messages));
                             return Unauthorized();
 
                         }
+                    },
+                    Fail: (messages, notices) =>
+                    {
+                        _logger.LogNotice(notices);
+                        return notices.HasFlag(Flag.SecurityBreach) ? Forbid() : StatusCode(StatusCodes.Status500InternalServerError, messages.Join());
+                    });
             }
             catch(Exception ex)
             {
-                _logger.LogError(ex, MessageKey.UnexpectedError.ToString());
+                _logger.LogEnvelopeError(envelopeEeceiverId: envelopeReceiverId, exception: ex);
-                return this.InnerServiceError(messageKey: MessageKey.UnexpectedError);
+                return this.InnerServiceError(message: _localizer[MessageKey.UnexpectedError]);
             }
         }
 
@@ -186,21 +178,25 @@ namespace EnvelopeGenerator.Web.Controllers
         {
             try
             {
-                var result = await _envRcvService.IsExisting(envelopeReceiverId: envelopeReceiverId);
+                return await _envRcvService.IsExisting(envelopeReceiverId: envelopeReceiverId).ThenAsync(
-                bool isExisting = result.Data;
+                    SuccessAsync: async isExisting =>
-                if (result.HasFlag(EnvelopeFlag.NonDecodableEnvelopeReceiverId) || !isExisting)
+                    {
+                        if(!isExisting)
                             return this.ViewEnvelopeNotFound();
 
                         EnvelopeResponse response = await envelopeOldService.LoadEnvelope(envelopeReceiverId);
-
                         if (!envelopeOldService.ReceiverAlreadySigned(response.Envelope, response.Receiver.Id))
-                {
                             return Redirect($"/EnvelopeKey/{envelopeReceiverId}/Locked");
-                }
 
                         await HttpContext.SignOutAsync(CookieAuthenticationDefaults.AuthenticationScheme);
                         ViewData["EnvelopeKey"] = envelopeReceiverId;
                         return View();
+                    },
+                    Fail: IActionResult (messages, notices) =>
+                    {
+                        _logger.LogNotice(notices);
+                        return this.ViewEnvelopeNotFound();
+                    });
             }
             catch (Exception ex)
             {

EnvelopeGenerator.Web/Controllers/Test/TestConfigController.cs

@@ -6,7 +6,7 @@ using EnvelopeGenerator.Infrastructure.Contracts;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestConfigController : TestControllerBase<TestConfigController, IConfigService, IConfigRepository, ConfigDto, Config, int>
+    public class TestConfigController : TestControllerBase<IConfigService, IConfigRepository, ConfigDto, Config, int>
     {
         public TestConfigController(ILogger<TestConfigController> logger, IConfigService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestControllerBase.cs

@@ -7,9 +7,12 @@ namespace EnvelopeGenerator.Web.Controllers.Test
 {
     [ApiController]
     [Route("api/test/[controller]")]
-    public class TestControllerBase<TOriginalController, TCRUDService, TCRUDRepository, TDto, TEntity, TId> : BasicCRUDControllerBase<TOriginalController, TCRUDService, TCRUDRepository, TDto, TEntity, TId> where TOriginalController : CRUDControllerBase<TOriginalController, TCRUDService, TCRUDRepository, TDto, TDto, TDto, TEntity, TId> where TCRUDService : ICRUDService<TCRUDRepository, TDto, TDto, TDto, TEntity, TId> where TCRUDRepository : ICRUDRepository<TEntity, TId> where TDto : class where TEntity : class
+    public class TestControllerBase<TCRUDService, TCRUDRepository, TDto, TEntity, TId> : BasicCRUDControllerBase<TCRUDService, TCRUDRepository, TDto, TEntity, TId> 
+        where TCRUDService : ICRUDService<TCRUDRepository, TDto, TDto, TDto, TEntity, TId>
+        where TCRUDRepository : ICRUDRepository<TEntity, TId> 
+        where TDto : class where TEntity : class
     {
-        public TestControllerBase(ILogger<TOriginalController> logger, TCRUDService service) : base(logger, service)
+        public TestControllerBase(ILogger logger, TCRUDService service) : base(logger, service)
         {
         }
     }

EnvelopeGenerator.Web/Controllers/Test/TestDocumentReceiverElementController.cs

@@ -6,7 +6,7 @@ using EnvelopeGenerator.Infrastructure.Contracts;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestDocumentReceiverElementController : TestControllerBase<TestDocumentReceiverElementController, IDocumentReceiverElementService, IDocumentReceiverElementRepository, DocumentReceiverElementDto, DocumentReceiverElement, int>
+    public class TestDocumentReceiverElementController : TestControllerBase<IDocumentReceiverElementService, IDocumentReceiverElementRepository, DocumentReceiverElementDto, DocumentReceiverElement, int>
     {
         public TestDocumentReceiverElementController(ILogger<TestDocumentReceiverElementController> logger, IDocumentReceiverElementService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestDocumentStatusController.cs

@@ -6,7 +6,7 @@ using EnvelopeGenerator.Infrastructure.Contracts;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestDocumentStatusController : TestControllerBase<TestDocumentStatusController, IDocumentStatusService, IDocumentStatusRepository, DocumentStatusDto, DocumentStatus, int>
+    public class TestDocumentStatusController : TestControllerBase<IDocumentStatusService, IDocumentStatusRepository, DocumentStatusDto, DocumentStatus, int>
     {
         public TestDocumentStatusController(ILogger<TestDocumentStatusController> logger, IDocumentStatusService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestEmailTemplateController.cs

@@ -5,7 +5,7 @@ using EnvelopeGenerator.Infrastructure.Contracts;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestEmailTemplateController : TestControllerBase<TestEmailTemplateController, IEmailTemplateService, IEmailTemplateRepository, EmailTemplateDto, EmailTemplate, int>
+    public class TestEmailTemplateController : TestControllerBase<IEmailTemplateService, IEmailTemplateRepository, EmailTemplateDto, EmailTemplate, int>
     {
         public TestEmailTemplateController(ILogger<TestEmailTemplateController> logger, IEmailTemplateService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestEnvelopeCertificateController.cs

@@ -6,7 +6,7 @@ using EnvelopeGenerator.Infrastructure.Contracts;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestEnvelopeCertificateController : TestControllerBase<TestEnvelopeCertificateController, IEnvelopeCertificateService, IEnvelopeCertificateRepository, EnvelopeCertificateDto, EnvelopeCertificate, int>
+    public class TestEnvelopeCertificateController : TestControllerBase<IEnvelopeCertificateService, IEnvelopeCertificateRepository, EnvelopeCertificateDto, EnvelopeCertificate, int>
     {
         public TestEnvelopeCertificateController(ILogger<TestEnvelopeCertificateController> logger, IEnvelopeCertificateService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestEnvelopeController.cs

@@ -7,7 +7,7 @@ using Microsoft.AspNetCore.Mvc;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestEnvelopeController : TestControllerBase<TestEnvelopeController, IEnvelopeService, IEnvelopeRepository, EnvelopeDto, Envelope, int>
+    public class TestEnvelopeController : TestControllerBase<IEnvelopeService, IEnvelopeRepository, EnvelopeDto, Envelope, int>
     {
         public TestEnvelopeController(ILogger<TestEnvelopeController> logger, IEnvelopeService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestEnvelopeDocumentController.cs

@@ -6,7 +6,7 @@ using EnvelopeGenerator.Infrastructure.Contracts;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestEnvelopeDocumentController : TestControllerBase<TestEnvelopeDocumentController, IEnvelopeDocumentService, IEnvelopeDocumentRepository, EnvelopeDocumentDto, EnvelopeDocument, int>
+    public class TestEnvelopeDocumentController : TestControllerBase<IEnvelopeDocumentService, IEnvelopeDocumentRepository, EnvelopeDocumentDto, EnvelopeDocument, int>
     {
         public TestEnvelopeDocumentController(ILogger<TestEnvelopeDocumentController> logger, IEnvelopeDocumentService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestEnvelopeHistoryController.cs

@@ -7,7 +7,7 @@ using Microsoft.AspNetCore.Mvc;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestEnvelopeHistoryController : TestControllerBase<TestEnvelopeHistoryController, IEnvelopeHistoryService, IEnvelopeHistoryRepository, EnvelopeHistoryDto, EnvelopeHistory, long>
+    public class TestEnvelopeHistoryController : TestControllerBase<IEnvelopeHistoryService, IEnvelopeHistoryRepository, EnvelopeHistoryDto, EnvelopeHistory, long>
     {
         public TestEnvelopeHistoryController(ILogger<TestEnvelopeHistoryController> logger, IEnvelopeHistoryService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestEnvelopeReceiverController.cs

@@ -9,7 +9,7 @@ using Microsoft.AspNetCore.Mvc;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestEnvelopeReceiverController : TestControllerBase<TestEnvelopeReceiverController, IEnvelopeReceiverService, IEnvelopeReceiverRepository, EnvelopeReceiverDto, EnvelopeReceiver, int>
+    public class TestEnvelopeReceiverController : TestControllerBase<IEnvelopeReceiverService, IEnvelopeReceiverRepository, EnvelopeReceiverDto, EnvelopeReceiver, int>
     {
         public TestEnvelopeReceiverController(ILogger<TestEnvelopeReceiverController> logger, IEnvelopeReceiverService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestEnvelopeTypeController.cs

@@ -6,7 +6,7 @@ using EnvelopeGenerator.Infrastructure.Contracts;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestEnvelopeTypeController : TestControllerBase<TestEnvelopeTypeController, IEnvelopeTypeService, IEnvelopeTypeRepository, EnvelopeTypeDto, EnvelopeType, int>
+    public class TestEnvelopeTypeController : TestControllerBase<IEnvelopeTypeService, IEnvelopeTypeRepository, EnvelopeTypeDto, EnvelopeType, int>
     {
         public TestEnvelopeTypeController(ILogger<TestEnvelopeTypeController> logger, IEnvelopeTypeService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestReceiverController.cs

@@ -6,7 +6,7 @@ using EnvelopeGenerator.Infrastructure.Contracts;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestReceiverController : TestControllerBase<TestReceiverController, IReceiverService, IReceiverRepository, ReceiverDto, Receiver, int>
+    public class TestReceiverController : TestControllerBase<IReceiverService, IReceiverRepository, ReceiverDto, Receiver, int>
     {
         public TestReceiverController(ILogger<TestReceiverController> logger, IReceiverService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestUserReceiverController.cs

@@ -6,7 +6,7 @@ using EnvelopeGenerator.Infrastructure.Contracts;
 
 namespace EnvelopeGenerator.Web.Controllers.Test
 {
-    public class TestUserReceiverController : TestControllerBase<TestUserReceiverController, IUserReceiverService, IUserReceiverRepository, UserReceiverDto, UserReceiver, int>
+    public class TestUserReceiverController : TestControllerBase< IUserReceiverService, IUserReceiverRepository, UserReceiverDto, UserReceiver, int>
     {
         public TestUserReceiverController(ILogger<TestUserReceiverController> logger, IUserReceiverService service) : base(logger, service)
         {

EnvelopeGenerator.Web/Controllers/Test/TestViewController.cs

@@ -9,14 +9,10 @@ namespace EnvelopeGenerator.Web.Controllers.Test
     {
         private readonly EnvelopeOldService envelopeOldService;
         private readonly IConfiguration _config;
-        private readonly IEnvelopeReceiverService _envRcvService;
-        private readonly IEnvelopeService _envelopeService;
 
-        public TestViewController(DatabaseService databaseService, EnvelopeOldService envelopeOldService, ILogger<TestViewController> logger, IConfiguration configuration, IEnvelopeReceiverService envelopeReceiverService, IEnvelopeService envelopeService) : base(databaseService, logger)
+        public TestViewController(DatabaseService databaseService, EnvelopeOldService envelopeOldService, ILogger<TestViewController> logger, IConfiguration configuration) : base(databaseService, logger)
         {
             this.envelopeOldService = envelopeOldService;
-            _envRcvService = envelopeReceiverService;
-            _envelopeService = envelopeService;
             _config = configuration;
         }
 

EnvelopeGenerator.Web/MessageKey.cs

@@ -1,12 +1,12 @@
 namespace EnvelopeGenerator.Web
 {
-    public enum MessageKey
+    public static class MessageKey
     {
-        ServiceOutputNullError,
+        public static readonly string ServiceOutputNullError = "ServiceOutputNullError";
-        UnexpectedError,
+        public static readonly string UnexpectedError = "UnexpectedError";
-        FailedToSendAccessCode,
+        public static readonly string FailedToSendAccessCode = "FailedToSendAccessCode";
-        WrongEnvelopeReceiverId, //the value should be about URL (like URL is not existing) as a part of security.
+        public static readonly string WrongEnvelopeReceiverId = "WrongEnvelopeReceiverId";
-        DataIntegrityError,
+        public static readonly string DataIntegrityError = "DataIntegrityError";
-        NonDecodableEnvelopeReceiverId
+        public static readonly string NonDecodableEnvelopeReceiverId = "NonDecodableEnvelopeReceiverId";
     }
 }

EnvelopeGenerator.Web/Views/Home/ShowEnvelope.cshtml

@@ -1,27 +1,26 @@
 @using DigitalData.Core.DTO;
 @using EnvelopeGenerator.Application.DTOs;
-@model DataResult<EnvelopeDto>;
+@model EnvelopeReceiverDto;
 @{
     ViewData["Title"] = "Dokument unterschreiben";
 }
 <partial name="_CookieConsentPartial" />
-@if (Model.IsSuccess && Model.Data is not null)
+@{
-{
+    var envelope = Model.Envelope;
-    var envelope = Model.Data;
+    var document = Model.Envelope?.Documents?.FirstOrDefault();
-    var document = envelope.Documents?.FirstOrDefault();
+    var receiver = Model.Envelope?.EnvelopeReceivers?.FirstOrDefault();
-    var receiver = envelope.EnvelopeReceivers?.FirstOrDefault();
+    var sender = Model.Envelope?.User;
-    var sender = envelope.User;
     var receiverName = receiver?.Name ?? string.Empty;
     var pages = document?.Elements?.Select(e => e.Page) ?? Array.Empty<int>();
     var stPageIndexes = string.Join(pages.Count() > 1 ? ", " : "", pages.Take(pages.Count() - 1))
                   + (pages.Count() > 1 ? " und " : "") + pages.LastOrDefault();
-
+}
 <nav class="navbar navbar-light bg-light">
     <div class="container-fluid">
         <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarToggleExternalContent" aria-controls="navbarToggleExternalContent" aria-expanded="false" aria-label="Toggle navigation">
             <span class="navbar-toggler-icon"></span>
         </button>
-            <div class="navbar-brand me-auto ms-5 envelope-message">@($"Hallo {receiverName}, {@envelope.Message}")</div>
+            <div class="navbar-brand me-auto ms-5 envelope-message">@($"Hallo {receiverName}, {@envelope?.Message}")</div>
         <div class="col-1  p-0 m-0 me-3 d-flex">
             <img src="~/img/digital_data.svg" alt="...">
         </div>
@@ -36,16 +35,15 @@
                 </div>
                 <div class="col p-0 m-0">
                     <div class="card-body p-0 m-0">
-                        <h5 class="card-title p-0 m-0">@($"{envelope.Title}")</h5>
+                        <h5 class="card-title p-0 m-0">@($"{envelope?.Title}")</h5>
                         <p class="card-text p-0 m-0">@($"Sie haben {(pages.Count())} Briefe zu unterschreiben. Bitte prüfen Sie die Seiten {stPageIndexes}.")</p>
-                            <p class="card-text p-0 m-0"><small class="text-body-secondary">Erstellt am @envelope.AddedWhen von @sender?.Prename @sender?.Name. Sie können den Absender über <a href="mailto:@(sender?.Email)?subject=@(envelope.Title)&body=Sehr%20geehrter%20@(sender?.Prename)%20@(sender?.Name),%0A%0A%0A">@sender?.Email</a> kontaktieren.</small></p>
+                            <p class="card-text p-0 m-0"><small class="text-body-secondary">Erstellt am @envelope.?AddedWhen von @sender?.Prename @sender?.Name. Sie können den Absender über <a href="mailto:@(sender?.Email)?subject=@(envelope?.Title)&body=Sehr%20geehrter%20@(sender?.Prename)%20@(sender?.Name),%0A%0A%0A">@sender?.Email</a> kontaktieren.</small></p>
                     </div>
                 </div>
             </div>
         </div>
     </div>
 </div>
-}
 <script>
     const collapseNav = () => {
         document.addEventListener('click', function (event) {