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Alex
Alex

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.NET Learning Notes: How to use FluentValidation and Custom attributes to check parameters

Reference:
https://docs.fluentvalidation.net/en/latest/installation.html
https://learn.microsoft.com/en-us/aspnet/core/mvc/models/validation?view=aspnetcore-9.0

Thanks for providing learning code from Zack.Yang

FluentValidation is a .NET library for building strongly-typed validation rules.

The FluentValidation.AspNetCore package is no longer being maintained and is now unsupported. We encourage users move away from this package and use the core FluentValidation package with a manual validation

1.Install NuGet package:

FluentValidation
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if you want to let FluentValidation automatically find all the validators in a specific assembly using an extension method. You should install another NuGet package:

FluentValidation.DependencyInjectionExtensions
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2.Register validators

services.AddScoped<IValidator<Person>, PersonValidator>();
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Or (DependencyInjectionExtensions)

services.AddValidatorsFromAssemblyContaining<UserValidator>();
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3.Define a set of validation rules for a class(e.g. Person) by inheriting from AbstractValidator

public class Person { public int Id { get; set; } public string Name { get; set; } public string Email { get; set; } public int Age { get; set; } } public class PersonValidator : AbstractValidator<Person> { public PersonValidator() { RuleFor(p => p.Id).NotNull(); RuleFor(p => p.Name).Length(5, 10); RuleFor(p => p.Email).EmailAddress(); RuleFor(p => p.Age).InclusiveBetween(18, 60); // if the field is a complex properties, you can set another // validator for it // RuleFor(p => p.Address).SetValidator(new AddressValidator) } }
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4.Manual Validation

[HttpPost] public IActionResult Validate([GuidValidator]Guid guid, Person person) { var result = validator.Validate(person); if (!result.IsValid) { result.AddToModelState(this.ModelState); return BadRequest(ModelState); } return Ok("Validate person ok"); }
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Besides, For scenarios that the build-in validation attributes don't handle, you can create custom validation attributes.
1.Create a class that inherits from ValidationAttribute, and override the IsValid method

public class GuidValidatorAttribute : ValidationAttribute { public const string DefaultErrorMessage = "The {0} field is required and not Guid.Empty"; public GuidValidatorAttribute() : base(DefaultErrorMessage) { } public override bool IsValid(object? value) { if (value is not null && value is Guid) { Guid guid = (Guid)value; return guid != Guid.Empty; } else { return false; } } }
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2.Add this attribute to parameter

public IActionResult Validate([GuidValidator]Guid guid, Person person) { }
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