Witness

Witness is a small vaidation library for .NET Core that allows building object validation in a fluent style. It is mostly targets custom validation rules that are very hard to implement in existing solutions like Fluent Validation.

Features:

• Fully fluent-style based on pure functions
• DI inside validation rules
• Conditional branches with .If

Get Started

Witness can be installed using the Nuget package manager or the dotnet CLI.

dotnet add package WitnessValidation

If you need to use DI for validation add the following package:

dotnet add package WitnessValidation.DependencyInjectionExtensions

Example

using Witness;

public class Person
{
    public string FirstName { get; set; }

    public string LastName { get; set; }
    
    public uint Age { get; set; }
    
    public string GithubAccount { get; set; }
}


public static class PersonValidationRulesExtensions
{    
    [Pure]
    public static Func<IValidationContext<Person, string>> ShouldExistInGithub(this Func<IValidationContext<Person, string>> context)
    {
        return () =>
        {
            var c = context();

            bool isValid = !string.IsNullOrEmpty(c.OUV);
            if (isValid)
            {
                using HttpClient client = new HttpClient();
                var result = new TaskFactory(TaskScheduler.Current)
                    .StartNew(async () => await client.GetAsync($"https://github.com/{c.OUV}"))
                    .Unwrap()
                    .GetAwaiter()
                    .GetResult();

                isValid = result.StatusCode != HttpStatusCode.NotFound;
            }

            if (!isValid)
            {
                c.ValidationErrors.Add($"{c.OUVName} should be a valid Github username");
            }

            return c;
        };
    }
}

Person person = new Person()
{
    FirstName = "Joe",
    LastName = string.Empty,
    Age = 5,
    GithubAccount = "test",
};

var result = person
    .Validate()
    .RuleFor(c => c.FirstName).ShouldNotBeEmptyOrNull()
    .And()
    .RuleFor(c => c.LastName).ShouldNotBeEmptyOrNull()
    .And()
    .RuleFor(c => c.Age).ShouldBeInRange(18, 100)
    .And()
    .RuleFor(c => c.GithubAccount).ShouldExistInGithub()
    .Execute();

DI Example

public static class PersonValidationRulesExtensions
{
    [Pure]
    public static Func<IValidationContext<Person, string>> ShouldExistInGithub(this Func<IValidationContext<Person, string>> context)
    {
        return () =>
        {
            var c = context();

            bool isValid = !string.IsNullOrEmpty(c.OUV);
            if (isValid)
            {
                var githubService = c.Resolve<IGithubService>();
                isValid = githubService.IsUserExists(c.OUV);
            }

            if (!isValid)
            {
                c.ValidationErrors.Add($"{c.OUVName} should be a valid Github username");
            }

            return c;
        };
    }
}

Person person = new Person()
{
    FirstName = "Joe",
    LastName = string.Empty,
    Age = 5,
    GithubAccount = "test",
};

var serviceProviderCollection = new ServiceCollection();
serviceProviderCollection.AddTransient<IGithubService, GithubService>();
IServiceProvider serviceProvider = serviceProviderCollection.BuildServiceProvider();

var result = person
    .Validate()
    .WithServiceProvider(serviceProvider)
    .FirstName().ShouldNotBeEmptyOrNull()
    .And()
    .LastName().ShouldNotBeEmptyOrNull()
    .And()
    .Age().ShouldBeInRange(18, 100)
    .And()
    .GithubAccount().ShouldExistInGithub()
    .Execute();