Quick start

1. Install

dotnet add package Valiant.Validation

For an application integration, install the most specific package instead. For example, Valiant.Validation.AspNetCore carries the core runtime, build, and analyzer assets needed to generate validators.

2. Declare a validator

using Valiant.Validation;

public sealed record RegisterUser(string? Name, int Age);

[ValiantValidator]
public sealed partial class RegisterUserValidator
    : ValidatorDefinition<RegisterUser>
{
    public override void Configure(ValidationContext<RegisterUser> context)
    {
        context.Property(request => request.Name)
            .Required("NameRequired", "Enter a name.")
            .MaxLength(64);

        context.Property(request => request.Age)
            .GreaterThanOrEqualTo(18);
    }
}

The declaration must be partial and marked with [ValiantValidator]. The generator emits IValidator<RegisterUser> directly on the class.

3. Validate

IValidator<RegisterUser> validator = new RegisterUserValidator();
ValidationResult result = validator.Validate(new RegisterUser(null, 16));

if (!result.IsValid)
{
    foreach (var failure in result.Errors)
    {
        Console.WriteLine($"{failure.PropertyName}: {failure.ErrorMessage}");
    }
}

Use ValidateAsync for validators that contain async rules. Convenience APIs include IsValid, IsValidAsync, and ThrowIfFailed on the result.

4. Register generated validators

using Valiant.Validation.DependencyInjection;

builder.Services.AddValiantValidators(options =>
{
    options.Mode = ValiantValidationMode.Auto;
    options.FailureBehavior = ValiantFailureBehavior.ValidateAll;
    options.Lifetime = ValiantValidatorLifetime.Scoped;
});

Inject IValidator<RegisterUser> wherever the request is handled.

Async rule safety

Call ValidateAsync when a validator or reused property validator may perform asynchronous work. The synchronous API does not silently block on async validation.