1. Getting started

Lite and simple validation library based on composition. It aims to simplify the composition and reuse of validations logics. You create single and simple validations, and then you add those validations to validate an entire model.

Compositing validation:

ICompositeValidation<Person> Validation = new CompositeValidation<Person>()
       .NotNull(nameof(Person.FirstName), x => x.FirstName) 
       .MinimumLength(nameof(Person.FirstName), x => x.FirstName, 3) 
       .MaximumLength(nameof(Person.FirstName), x => x.FirstName, 10) 
       .Email(nameof(Person.Email), x => x.Email) 
       .RegEx(nameof(Person.Phone), x => x.Phone, @"^[0-9\-\+]{9,15}$") 
       .MustNot(nameof(Person.BirthDate), x => x.BirthDate, x => x.Year < 1850) 
       .Must(nameof(Person.BirthDate), x => x.BirthDate, x => x < DateTime.Now) 
       .Add(new CustomValidation(nameof(Person)), x => x);        

Validating the model:

if (!Validation.Update(person).IsValid)
{
   IReadOnlyCollection<Failure> failures = Validation.Failures;
}

Creating a custom validation:

public class CustomValidation : Validation<Person>
{
	private const string DefaultValidationMessage
		= "{0} - Person under 16 can not have drive license";

	public CustomValidation(
		string groupName, 
		Person target = default(Person), 
		string formatMessage = DefaultValidationMessage, 
		int severity = 1) 
		: base(groupName, target, formatMessage, severity)
	{
	}

	protected override IList<Failure> Validate()
	{
		var failures = new List<Failure>();
		if (Target.HasDriverLicense && Target.Age < 16)
		{
			failures.Add(new Failure(this));
		}

		return failures;
	}
}