FluentValidation–Conditional Validation Rule

FluentValidation is really powerful, but this power also makes it sometimes complex to find the correct way to solve a specific problem. In this case I wanted to conditionally execute a certain validation when data in another field was filled in.

FluentValidation makes this possible through the usage of the When/Unless methods. Here is a short example:

	RuleFor(x => x.FastDelivery)
	.NotEmpty()
	.WithState(x => new ValidationState() {
	Code = "FastDelivery.empty",
	Keys = { ValidationKeys.Delivery }
	});
	RuleFor(x => x.DeliveryDate)
	.NotEmpty()
	.WithState(x => new ValidationState()
	{
	Code = "DeliveryDate.empty",
	Keys = { ValidationKeys.Delivery }
	})
	.When(x=> x.FastDelivery == true);

view raw FluentValidationConditionalcheck.cs hosted with ❤ by GitHub

We only validate the DeliveryDate when FastDelivery is choosen.