(B) Link validation, implement Create employee case

Clinics.Backend/API/API.csproj

@@ -7,6 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="11.9.2" />
     <PackageReference Include="MediatR" Version="12.4.0" />
     <PackageReference Include="Microsoft.EntityFrameworkCore" Version="8.0.8" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="8.0.8">

Clinics.Backend/API/Program.cs

 using API.Options.Database;
 using API.SeedDatabaseHelper;
+using Application.Behaviors;
+using FluentValidation;
+using MediatR;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Options;
 using Persistence.Context;
@@ -49,6 +52,12 @@ builder
 #region Add MadiatR
 builder.Services.AddMediatR(configuration =>
     configuration.RegisterServicesFromAssembly(Application.AssemblyReference.Assembly));
+
+#region Add validation pipeline
+builder.Services.AddScoped(typeof(IPipelineBehavior<,>), typeof(ValidationPipelineBehavior<,>));
+builder.Services.AddValidatorsFromAssembly(Application.AssemblyReference.Assembly);
+#endregion
+
 #endregion
 
 #region Link controllers with presentation layer

Clinics.Backend/Application/Application.csproj

@@ -7,6 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="FluentValidation" Version="11.9.2" />
     <PackageReference Include="MediatR" Version="12.4.0" />
   </ItemGroup>
 

Clinics.Backend/Application/Behaviors/ValidationPipelineBehavior.cs

+using Domain.Shared.Validation;
+using Domain.Shared;
+using MediatR;
+using FluentValidation;
+
+namespace Application.Behaviors;
+
+// Using MediatR pipeline to perform validation
+// Using Fluent validation (IValidator) to make validators
+public class ValidationPipelineBehavior<TRequest, TResponse>
+    : IPipelineBehavior<TRequest, TResponse> // From MediatR
+    where TRequest : IRequest<TResponse> // Request sent by the pipeline (enforced by imp. of CQRS)
+    where TResponse : Result // Type of response (enforced by imp. of CQRS)
+{
+
+    #region CTOR DI for validators
+    private readonly IEnumerable<IValidator<TRequest>> _validators;
+    public ValidationPipelineBehavior(IEnumerable<IValidator<TRequest>> validators)
+    {
+        _validators = validators;
+    }
+    #endregion
+
+
+    #region Create validation result
+    private static TResult CreateValidationResult<TResult>(Error[] errors)
+        where TResult : Result
+    {
+        // Simple case, Result only
+        if (typeof(TResult) == typeof(Result))
+        {
+            return (ValidationResult.WithErrors(errors) as TResult)!;
+            // This won't fail ever
+        }
+
+        // Other complicated case, we have a Result<Type>
+        // Using reflection 
+        object validationResult = typeof(ValidationResult<>)
+            .GetGenericTypeDefinition()
+            .MakeGenericType(typeof(TResult).GenericTypeArguments[0])
+            .GetMethod(nameof(ValidationResult.WithErrors))!
+            .Invoke(null, [errors])!;
+
+        return (TResult)validationResult;
+    }
+
+    #endregion
+
+    #region Handle method (pipeline behavior)
+    public async Task<TResponse> Handle(
+        TRequest request,
+        RequestHandlerDelegate<TResponse> next,
+        CancellationToken cancellationToken)
+
+    {
+        // Validate request
+        // If any errors, return validation request
+        // Otherwise,return next() [Pipline ~ Middleware]
+
+        // Case of no validators
+        if (!_validators.Any())
+        {
+            return await next();
+        }
+
+        // Generate errors array
+
+        Error[] errors = _validators
+            .Select(validator => validator.Validate(request)) // Select the result of validate method
+            .SelectMany(validationResult => validationResult.Errors)
+            .Where(validationFailure => validationFailure is not null)
+            .Select(failure => new Error( // Project into Error object
+                failure.PropertyName,
+                failure.ErrorMessage))
+            .Distinct()
+            .ToArray();
+
+        if (errors.Length != 0)
+        {
+            return CreateValidationResult<TResponse>(errors);
+            // Static method in this class
+        }
+
+        return await next();
+    }
+    #endregion
+
+
+
+}

Clinics.Backend/Application/Employees/Commands/Create/CreateEmployeeCommandValidator.cs

+using Domain.ValidationConstants.ErrorMessages;
+using Domain.ValidationConstants.RegularExpressions;
+using FluentValidation;
+
+namespace Application.Employees.Commands.Create;
+
+public class CreateEmployeeCommandValidator : AbstractValidator<CreateEmployeeCommand>
+{
+    public CreateEmployeeCommandValidator()
+    {
+        #region First name
+        RuleFor(c => c.FirstName)
+            .NotEmpty()
+            .WithMessage(ValidationErrorMessages.Required);
+        RuleFor(c => c.FirstName)
+            .MaximumLength(50)
+            .WithMessage(ValidationErrorMessages.FixedLength);
+        RuleFor(c => c.FirstName)
+            .Matches(ValidationRegularExpressions.ArabicLettersOnly)
+            .WithMessage(ValidationErrorMessages.ArabicLettersOnly);
+        #endregion
+
+        #region Middle name
+        RuleFor(c => c.MiddleName)
+            .NotEmpty()
+            .WithMessage(ValidationErrorMessages.Required);
+        RuleFor(c => c.MiddleName)
+            .MaximumLength(50)
+            .WithMessage(ValidationErrorMessages.FixedLength);
+        RuleFor(c => c.MiddleName)
+            .Matches(ValidationRegularExpressions.ArabicLettersOnly)
+            .WithMessage(ValidationErrorMessages.ArabicLettersOnly);
+        #endregion
+
+        #region Last name
+        RuleFor(c => c.LastName)
+            .NotEmpty()
+            .WithMessage(ValidationErrorMessages.Required);
+        RuleFor(c => c.LastName)
+            .MaximumLength(50)
+            .WithMessage(ValidationErrorMessages.FixedLength);
+        RuleFor(c => c.LastName)
+            .Matches(ValidationRegularExpressions.ArabicLettersOnly)
+            .WithMessage(ValidationErrorMessages.ArabicLettersOnly);
+        #endregion
+
+        #region Serial number
+        RuleFor(c => c.SerialNumber)
+            .NotEmpty()
+            .WithMessage(ValidationErrorMessages.Required);
+        RuleFor(c => c.SerialNumber)
+            .Matches(ValidationRegularExpressions.NumbersOnly)
+            .WithMessage(ValidationErrorMessages.NumbersOnly);
+        RuleFor(c => c.SerialNumber)
+            .MaximumLength(20)
+            .WithMessage(ValidationErrorMessages.FixedLength);
+        #endregion
+
+        #region Center status
+        RuleFor(c => c.CenterStatus)
+            .NotEmpty()
+            .WithMessage(ValidationErrorMessages.Required);
+        RuleFor(c => c.CenterStatus)
+            .Matches(ValidationRegularExpressions.ArabicLettersOnly)
+            .WithMessage(ValidationErrorMessages.ArabicLettersOnly);
+        RuleFor(c => c.CenterStatus)
+            .MaximumLength(50)
+            .WithMessage(ValidationErrorMessages.FixedLength);
+        #endregion
+
+        // TODO: add validation rules for additional fields
+    }
+}

Clinics.Backend/Domain/ValidationConstants/ErrorMessages/ValidationErrorMessages.cs

+namespace Domain.ValidationConstants.ErrorMessages;
+
+public static class ValidationErrorMessages
+{
+    public static string Required
+        => "هذا الحقل مطلوب";
+
+    public static string ArabicOrEnglishLettersOnly
+        => "يجب أن يحوي هذا الحقل على أحرف عربية فقط أو أحرف انكليزية فقط ولا يحوي أي رموز أو أرقام";
+
+    public static string ArabicLettersOnly
+        => "يجب أن يحوي هذا الحقل على أحرف عربية فقط ولا يحوي أي رموز أو أرقام";
+
+    public static string FixedLength
+        => "هذا الحقل طويل للغاية";
+
+    public static string NumbersOnly
+        => "يجب أن يحوي هذا الحقل على أرقام فقط";
+}

Clinics.Backend/Domain/ValidationConstants/RegularExpressions/ValidationRegularExpressions.cs

+namespace Domain.ValidationConstants.RegularExpressions;
+
+public static class ValidationRegularExpressions
+{
+    public static string ArabicOrEnglishLettersOnly
+        => @"^[\u0600-\u06ff\s]+$|^[a-zA-Z\s]+$";
+
+    public static string ArabicLettersOnly
+        => @"^[א-׿ء-ي]+$";
+
+    public static string EmailAddress
+        => @"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$";
+
+    public static string NumbersOnly
+        => @"^\d+$";
+
+
+}

Clinics.Backend/Presentation/Controllers/Base/ApiController.cs

+using Domain.Shared.Validation;
+using Domain.Shared;
+using MediatR;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Presentation.Controllers.Base;
+
+[ApiController]
+public abstract class ApiController : ControllerBase
+{
+
+    #region CTOR DI for MediatR sendse
+    protected readonly ISender _sender;
+
+    protected ApiController(ISender sender)
+    {
+        _sender = sender;
+    }
+    #endregion
+
+    protected IActionResult HandleFailure(Result result) =>
+        result switch
+        {
+            { IsSuccess: true } => throw new InvalidOperationException(),
+            IValidationResult validationResult =>
+                BadRequest(
+                    CreateProblemDetails(
+                        "Validation Error", StatusCodes.Status400BadRequest,
+                        result.Error,
+                        validationResult.Errors)),
+            _ =>
+                BadRequest(
+                    CreateProblemDetails(
+                        "Bad Request",
+                        StatusCodes.Status400BadRequest,
+                        result.Error))
+        };
+
+    private static ProblemDetails CreateProblemDetails(
+        string title,
+        int status,
+        Error error,
+        Error[]? errors = null) =>
+        new()
+        {
+            Title = title,
+            Type = error.Code,
+            Detail = error.Message,
+            Status = status,
+            Extensions = { { nameof(errors), errors } }
+        };
+}
\ No newline at end of file

Clinics.Backend/Presentation/Controllers/EmployeesController.cs

 using Application.Employees.Commands.Create;
 using MediatR;
 using Microsoft.AspNetCore.Mvc;
+using Presentation.Controllers.Base;
 
 namespace Presentation.Controllers;
 
-[Route("api/[controller]")]
-[ApiController]
-public class EmployeesController : ControllerBase
+[Route("api/Employees")]
+public class EmployeesController : ApiController
 {
+
     #region DI for MeditR sender
-    private readonly ISender _sender;
-    public EmployeesController(ISender sender)
+    public EmployeesController(ISender sender) : base(sender)
     {
-        _sender = sender;
     }
     #endregion
 
@@ -21,8 +20,8 @@ public class EmployeesController : ControllerBase
     public async Task<IActionResult> Create(CreateEmployeeCommand command)
     {
         var result = await _sender.Send(command);
-        if (result.IsSuccess)
+        if (result.IsFailure)
+            return HandleFailure(result);
         return Created();
-        else return BadRequest(result.Error.Message);
     }
 }