I've been putting some thought into validation in the context of an MVC Framework application. Recently I wrote about using Extension Method Validators as a neat way of expressing validation rules in your domain entities. These validators throw a ValidationException when they trigger.

sutekishopValidationErrors

Now in a user interface we would really like to see all the validation failures for a form. So we need to collect the exceptions as they occur and then continue processing. Here's a neat little Validator class that's simply a collection of Action delegates that executes them when its Validate method is called:

public class Validator : List<Action>
{
 public void Validate()
 {
 StringBuilder message = new StringBuilder();
 foreach (Action validation in this)
 {
 try
 {
 validation();
 }
 catch (ValidationException validationException)
 {
 message.AppendFormat("{0}<br />", validationException.Message);
 }
 }
 if (message.Length > 0)
 {
 throw new ValidationException(message.ToString());
 }
 }
}

You can use it like this:

string property = "";
Validator validator = new Validator
{
 () => property.Label("Property 1").IsRequired(),
 () => property.Label("Property 2").IsRequired(),
 () => property.Label("Property 3").IsRequired()
};
validator.Validate();

Since the 'property' variable is an empty string, each call to IsRequired() will throw a ValidationException. The message of each of these exceptions gets captured and then a single ValidationException will be called with the concatenated messages.