Replace custom ValidationBuilder with FluentValidation

.claude/skills/minimal-api/references/patterns.md

@@ -363,24 +363,37 @@ public static class ProductsPermissions
 
 ## Validation Classes
 
+Use FluentValidation `AbstractValidator<T>`. The framework provides a `ToValidationErrors()` extension that converts FluentValidation's `ValidationResult` to the `Dictionary<string, string[]>` shape consumed by `ValidationException` and the RFC 7807 response writer.
+
 ```csharp
-public static class CreateRequestValidator
+public sealed class CreateRequestValidator : AbstractValidator<CreateProductRequest>
 {
-    public static ValidationResult Validate(CreateProductRequest request) =>
-        new ValidationBuilder()
-            .AddErrorIf(
-                string.IsNullOrWhiteSpace(request.Name),
-                "Name",
-                "Product name is required."
-            )
-            .AddErrorIf(request.Price <= 0, "Price", "Price must be greater than zero.")
-            .Build();
+    public CreateRequestValidator()
+    {
+        RuleFor(x => x.Name).NotEmpty().WithMessage("Product name is required.");
+        RuleFor(x => x.Price).GreaterThan(0).WithMessage("Price must be greater than zero.");
+    }
 }
 ```
 
-Usage in endpoint:
+Register once per module in `ConfigureServices`:
+
 ```csharp
-var validation = CreateRequestValidator.Validate(request);
-if (!validation.IsValid)
-    throw new ValidationException(validation.Errors);
+services.AddValidatorsFromAssemblyContaining<ThisModule>();
+```
+
+Usage in endpoint (async lambda, inject `IValidator<TRequest>`):
+
+```csharp
+async (
+    CreateProductRequest request,
+    IValidator<CreateProductRequest> validator,
+    IProductContracts contracts
+) =>
+{
+    var validation = await validator.ValidateAsync(request);
+    if (!validation.IsValid)
+        throw new Core.Exceptions.ValidationException(validation.ToValidationErrors());
+    // ...
+}
 ```

.claude/skills/simplemodule/references/endpoints.md

@@ -150,14 +150,29 @@ var body = await JsonSerializer.DeserializeAsync<MyType>(context.Request.Body);
 
 ## Validation
 
+Use FluentValidation `AbstractValidator<T>`. Register via `services.AddValidatorsFromAssemblyContaining<YourModule>()` in `ConfigureServices`. Inject `IValidator<TRequest>` into the endpoint handler.
+
 ```csharp
-public static class CreateRequestValidator
+public sealed class CreateRequestValidator : AbstractValidator<CreateProductRequest>
+{
+    public CreateRequestValidator()
+    {
+        RuleFor(x => x.Name).NotEmpty().WithMessage("Product name is required.");
+        RuleFor(x => x.Price).GreaterThan(0).WithMessage("Price must be greater than zero.");
+    }
+}
+
+// In the endpoint lambda:
+async (
+    CreateProductRequest request,
+    IValidator<CreateProductRequest> validator,
+    IProductContracts products
+) =>
 {
-    public static ValidationResult Validate(CreateProductRequest request) =>
-        new ValidationBuilder()
-            .AddErrorIf(string.IsNullOrWhiteSpace(request.Name), "Name", "Product name is required.")
-            .AddErrorIf(request.Price <= 0, "Price", "Price must be greater than zero.")
-            .Build();
+    var validation = await validator.ValidateAsync(request);
+    if (!validation.IsValid)
+        throw new Core.Exceptions.ValidationException(validation.ToValidationErrors());
+    // ...
 }
 ```
 

Directory.Packages.props

@@ -60,6 +60,9 @@
     <PackageVersion Include="Cronos" Version="0.8.4" />
     <!-- Caching -->
     <PackageVersion Include="ZiggyCreatures.FusionCache" Version="2.6.0" />
+    <!-- Validation -->
+    <PackageVersion Include="FluentValidation" Version="12.1.1" />
+    <PackageVersion Include="FluentValidation.DependencyInjectionExtensions" Version="12.1.1" />
     <!-- Email -->
     <PackageVersion Include="MailKit" Version="4.15.1" />
     <!-- CLI -->

cli/SimpleModule.Cli/Templates/FeatureTemplates.cs

@@ -277,11 +277,7 @@ string singularName
                 var newBody = new List<string>
                 {
                     resultLines[braceStart], // opening brace
-                    "        var errors = new Dictionary<string, string[]>();",
-                    "",
-                    "        // TODO: add validation rules",
-                    "",
-                    "        return errors.Count > 0 ? ValidationResult.WithErrors(errors) : ValidationResult.Success;",
+                    "        // TODO: add validation rules via RuleFor(x => x.Prop)...",
                 };
 
                 // Keep the closing brace
@@ -369,20 +365,16 @@ private static string FallbackValidator(
         string singularName
     ) =>
         $$"""
-            using SimpleModule.Core.Validation;
+            using FluentValidation;
             using SimpleModule.{{moduleName}}.Contracts;
 
             namespace SimpleModule.{{moduleName}}.Endpoints.{{moduleName}};
 
-            public static class {{featureName}}RequestValidator
+            public sealed class {{featureName}}RequestValidator : AbstractValidator<{{singularName}}>
             {
-                public static ValidationResult Validate({{singularName}} request)
+                public {{featureName}}RequestValidator()
                 {
-                    var errors = new Dictionary<string, string[]>();
-
-                    // TODO: add validation rules
-
-                    return errors.Count > 0 ? ValidationResult.WithErrors(errors) : ValidationResult.Success;
+                    // TODO: add validation rules via RuleFor(x => x.Prop)...
                 }
             }
             """;

framework/SimpleModule.Core/SimpleModule.Core.csproj

@@ -8,5 +8,7 @@
     <FrameworkReference Include="Microsoft.AspNetCore.App" />
     <PackageReference Include="NetEscapades.EnumGenerators" PrivateAssets="all" />
     <PackageReference Include="ZiggyCreatures.FusionCache" />
+    <PackageReference Include="FluentValidation" />
+    <PackageReference Include="FluentValidation.DependencyInjectionExtensions" />
   </ItemGroup>
 </Project>

framework/SimpleModule.Core/Validation/ValidationResultExtensions.cs

@@ -0,0 +1,28 @@
+using FluentValidation.Results;
+
+namespace SimpleModule.Core.Validation;
+
+/// <summary>
+/// Bridges FluentValidation's <see cref="ValidationResult"/> to the
+/// <see cref="Dictionary{TKey,TValue}"/> shape consumed by
+/// <see cref="SimpleModule.Core.Exceptions.ValidationException"/> and
+/// the RFC 7807 <c>errors</c> extension written by <c>GlobalExceptionHandler</c>.
+/// </summary>
+public static class ValidationResultExtensions
+{
+    /// <summary>
+    /// Groups validation failures by property name, flattening their error
+    /// messages into a <c>string[]</c> per field.
+    /// </summary>
+    public static Dictionary<string, string[]> ToValidationErrors(this ValidationResult result)
+    {
+        ArgumentNullException.ThrowIfNull(result);
+        return result
+            .Errors.GroupBy(e => e.PropertyName, StringComparer.Ordinal)
+            .ToDictionary(
+                g => g.Key,
+                g => g.Select(e => e.ErrorMessage).ToArray(),
+                StringComparer.Ordinal
+            );
+    }
+}

modules/Email/src/SimpleModule.Email/EmailModule.cs

@@ -1,3 +1,4 @@
+using FluentValidation;
 using Microsoft.AspNetCore.Identity;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -23,6 +24,7 @@ public class EmailModule : IModule, IModuleServices
     public void ConfigureServices(IServiceCollection services, IConfiguration configuration)
     {
         services.AddModuleDbContext<EmailDbContext>(configuration, EmailConstants.ModuleName);
+        services.AddValidatorsFromAssemblyContaining<EmailModule>();
         var emailSection = configuration.GetSection("Email");
         services.Configure<EmailModuleOptions>(emailSection);
 

modules/Email/src/SimpleModule.Email/Endpoints/Messages/SendEmailEndpoint.cs

@@ -1,10 +1,11 @@
+using FluentValidation;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Routing;
 using SimpleModule.Core;
 using SimpleModule.Core.Authorization;
+using SimpleModule.Core.Validation;
 using SimpleModule.Email.Contracts;
-using SimpleModule.Email.Validators;
 
 namespace SimpleModule.Email.Endpoints.Messages;
 
@@ -16,11 +17,17 @@ public class SendEmailEndpoint : IEndpoint
     public void Map(IEndpointRouteBuilder app) =>
         app.MapPost(
                 Route,
-                async (SendEmailRequest request, IEmailContracts emailContracts) =>
+                async (
+                    SendEmailRequest request,
+                    IValidator<SendEmailRequest> validator,
+                    IEmailContracts emailContracts
+                ) =>
                 {
-                    var validation = SendEmailRequestValidator.Validate(request);
+                    var validation = await validator.ValidateAsync(request);
                     if (!validation.IsValid)
-                        throw new Core.Exceptions.ValidationException(validation.Errors);
+                        throw new Core.Exceptions.ValidationException(
+                            validation.ToValidationErrors()
+                        );
 
                     var message = await emailContracts.SendEmailAsync(request);
                     return TypedResults.Ok(message);