Fluent validation

Liens

• Fluent Validation
• Built-in Validators
• Fluent Validation on git
• Dynamic Validation with FluentValidation in WPF/MVVM

Exemple

var mc = new MyClass(); var validator = new MyClassValidator(); ValidationResult results = validator.Validate(mc); if (!results.IsValid) { foreach (var failure in results.Errors) { Console.WriteLine("Property " + failure.PropertyName + " failed validation. Error was: " + failure.ErrorMessage); } string allMessages = results.ToString(); Console.WriteLine(allMessages); } public sealed class MyClassValidator : AbstractValidator<MyClass> { public MyClassValidator() { this.RuleFor(x => x.Name) .NotNull() .Must(name => name != null) .Must(IsValid) .WithMessage("{PropertyName} is invalid."); // change error message. Default is: 'Name' must not be empty. } private static bool IsValid(string value) { return value != null; } } public sealed class MyClass { public int Id { get; set; } public string Name { get; set; } }

Output

{ "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1", "title": "One or more validation errors occurred.", "status": 400, "traceId": "|84df05e2-41e0d4841bb61293.", "errors": { "Name": [ "Name is invalid." ] } }

Built-in Validators

Enum Validator

Checks whether a numeric value is valid to be in that enum.

RuleFor(x => x.ErrorLevel).IsInEnum();

Set validator for complex properties

public sealed class MyClassValidator : AbstractValidator<MyClass> { public MyClassValidator() { RuleFor(mc => mc.MySubClass).SetValidator(new MySubClassValidator()); } } public sealed class MySubClassValidator : AbstractValidator<MySubClass> { public MySubClassValidator() { RuleFor(msc => msc.Name).NotNull(); } } public sealed class MyClass { public int Id { get; set; } public MySubClass MySubClass { get; set; } } public sealed class MySubClass { public int Id { get; set; } public string Name { get; set; } }

Validation on multiple properties

this.RuleFor(x => new { x.Property1, x.Property2 }) .Must(x => x.Property1.Count > 0 || x.Property2 .Count > 0) .OverridePropertyName(x => x.Property1);

Validate elements of a collection

If your root object is a collection, be aware that FV doesn't handle IReadOnlyCollection

public sealed class MyClassValidator : AbstractValidator<MyClass> { public MyClassValidator() { // use RuleForEach to apply rules on each element RuleForEach(x => x.Items) .NotEmpty() // use ChildRules for complex object .ChildRules(items => { items.RuleFor(x => x.Name).NotNull(); }); RuleForEach(mc => mc.Items) .SetValidator(new ItemValidator()); // use ForEach inside a RuleFor to apply rules on each element RuleFor(x => x.Ids) .NotEmpty() .ForEach(idRule => idRule.Must(x => x > 0)); RuleFor(x => x.Items) .NotEmpty() .ForEach(itemRule => itemRule.ChildRules(items => { items.RuleFor(x => x.Name).NotNull(); })); } } public sealed class MyClass { public List<int> Ids { get; } = new List<int>(); public List<Item> Items { get; } = new List<Item>(); } public sealed class Item { public string Name { get; set; } }

Conditions

When(x => x.Property > 0, () => { RuleFor(x => x.Name).NotNull(); }).Otherwise(() => { RuleFor(x => x.Name).MinimumLength(3); }); RuleFor(x => x.Name) .NotNull() .When(x => x.Property > 0); // code of length 4 or null RuleFor(x => x.Code) .Length(4) .Unless(x => string.IsNullOrEmpty(x.Code));

Overriding the error message

this.RuleFor(x => x.Name) .WithMessage("Error message on {PropertyName}.");

Placeholder
{PropertyName}	The name of the property being validated
{PropertyValue}	The value of the property being validated, these include the predicate validator (‘Must’ validator), the email and the regex validators.

Built-in Validators and their Placeholders

Custom message placeholders

ItemValidator.cs

public ItemValidator(IItemService itemService) { this.itemService = itemService; RuleFor(x => x).MustAsync(HasNoSimilarItemAsync) .OverridePropertyName("SimilarItem") .WithMessage("A similar item already exists. Name: {SimilarItemName} - Date: {SimilarItemDate:dd/MM/yyyy}"); } private async Task<bool> HasNoSimilarItemAsync( Item rootObject, Item item, PropertyValidatorContext context, CancellationToken token) { var similarItems = await itemService.FindSimilarItemsAsync(item); if (similarItems.Any()) { context.MessageFormatter.AppendArgument("SimilarItemName", similarItems[0].Name) .AppendArgument("SimilarItemDate", similarItems[0].Date); return false; } return true; }

Custom validator

RuleFor(x => x.Elements) .Custom((list, context) => { if(list.Count > 10) context.AddFailure("The list must contain 10 items or fewer"); } );

Cascade mode

// test first if Name is not null, then even if Name is null test if lenght is >= 3 RuleFor(x => x.Name) .NotNull() .MinimumLength(3); // test first if Name is not null, then only if Name is not null test if lenght is >= 3 RuleFor(x => x.Name) .Cascade(CascadeMode.Stop) .NotNull() .MinimumLength(3); // change the default cascade mode public MyClassValidator() { // First set the cascade mode RuleLevelCascadeMode = CascadeMode.Stop; RuleFor(x => x.Name).NotNull().MinimumLength(3);

Async Validation

var validator = new MyClassValidator(); var validationResult = await validator.ValidateAsync(myClass); public sealed class MyClassValidator : AbstractValidator<MyClass> { SomeExternalWebApiClient client; public MyClassValidator(SomeExternalWebApiClient client) { this.client = client; this.RuleFor(x => x.Name) .MustAsync(async (name, cancellation) => { bool nameExists = await client.NameExists(name); return !nameExists; }).WithMessage("Name is not valid."); } private static bool IsValid(string value) { return value != null; } }

Throwing Exceptions

try { validator.ValidateAndThrow(mc); } catch (ValidationException e) { foreach (var failure in e.Errors) { Console.WriteLine(failure.ErrorMessage); } }

ASP.NET Core integration

You should not use asynchronous rules when using ASP.NET automatic validation as ASP.NET’s validation pipeline is not asynchronous.

# install the nuget package dotnet add package FluentValidation.AspNetCore

Startup.cs

// automatic validation public void ConfigureServices(IServiceCollection services) { services.AddControllers() .AddFluentValidation(fv => { // automatic registration of the validators fv.RegisterValidatorsFromAssemblyContaining<PersonValidator>(); // disable other validator providers like DataAnnotations fv.RunDefaultMvcValidationAfterFluentValidationExecutes = false; }); // manual registration of the validators services.AddTransient<IValidator<Person>, PersonValidator>();

PersonController.cs

public class PersonController : Controller { [HttpPost] public IActionResult Create(Person person) { if(!ModelState.IsValid) { return BadRequest(ModelState); } // manual async validation var personValidator = new PersonValidator(); var validationResult = await personValidator.ValidateAsync(person); validationResult.AddToModelState(ModelState, null); if (!ModelState.IsValid) { return BadRequest(new ValidationProblemDetails(ModelState)); }

Use filter to check the model validity

Ainsi il n'est plus nécessaire de tester ModelState.IsValid dans chaque Controller.

App_Start\WebApiConfig.cs

public static void Register(HttpConfiguration config) { config.Filters.Add(new ValidateModelStateFilter());

ValidateModelStateFilter.cs

public class ValidateModelStateFilter : ActionFilterAttribute { public override void OnActionExecuting(HttpActionContext actionContext) { if (!actionContext.ModelState.IsValid) { actionContext.Response = actionContext.Request.CreateErrorResponse(HttpStatusCode.BadRequest, actionContext.ModelState);

Unit tests

MyValidatorTest.cs

public class MyValidatorTest { private readonly MyValidatorTest validator = new MyValidatorTest(); [Fact] public void ValidationOfProp3_AskProp1AndProp2_Error() { // Arrange var query = new MyQuery { Prop1 = "value1", Prop2 = "value2" }; // Act var result = this.validator.TestValidate(query); // Assert result.ShouldHaveValidationErrorFor(x => x.Prop3, query) .WithErrorCode(nameof(ValidationMessageResources.MyErrorMessage)) .WithErrorMessage(ValidationMessageResources.MyErrorMessage); }

WebApi 2 integration

Integration with ASP.NET WebApi 2 is no longer supported as of FluentValidation 9. Use ASP.NET Core. link

Installer le package NuGet FluentValidation.WebApi

Validator attribute

App_Start\WebApiConfig.cs

public static class WebApiConfig { public static void Register(HttpConfiguration config) { // ... FluentValidationModelValidatorProvider.Configure(config);

ItemController.cs

[HttpPost] [Route("")] [ResponseType(typeof(Item))] public IHttpActionResult Post(Item item) { // if the item is null, the validator is not executed if (item == null) { return this.BadRequest("Item cannot be null."); } // if there are validation errors if (!ModelState.IsValid) { return this.BadRequest(ModelState); }

Item.cs

// link the class with its validator [Validator(typeof(ItemValidator))] public sealed class Item { }

Dependency injection with Autofac

App_Start\WebApiConfig.cs

public static void Register(HttpConfiguration config) { var builder = new ContainerBuilder(); // register all the validator AssemblyScanner.FindValidatorsInAssembly(typeof(WebApiConfig).Assembly) .ForEach(result => { builder.RegisterType(result.ValidatorType).As(result.InterfaceType); }); // register the ValidatorFactory because its ctor needs an IComponentContext builder.RegisterType<AutofacValidatorFactory>(); IContainer container = builder.Build(); FluentValidationModelValidatorProvider.Configure(config, provider => { provider.ValidatorFactory = container.Resolve<AutofacValidatorFactory>(); });

AutofacValidatorFactory.cs

internal class AutofacValidatorFactory : ValidatorFactoryBase { private readonly IComponentContext context; public AutofacValidatorFactory(IComponentContext context) { this.context = context; } public override IValidator CreateInstance(Type validatorType) { if (this.context.TryResolve(validatorType, out var instance)) { var validator = instance as IValidator; return validator; } return null; } }