Postcode attribute

PostcodeAttribute.cs

/// <summary>
	/// Postcode validation attribute
	/// Must be uppercase with a single optional space
	/// </summary>
	[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
	public class PostcodeAttribute : DataTypeAttribute
	{
		private static readonly Regex _regex = new Regex(@"^(GIR ?0AA|[A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]([0-9ABEHMNPRV-Y])?)|[0-9][A-HJKPS-UW]) ?[0-9][ABD-HJLNP-UW-Z]{2})$");
		
		//if you need lowercase and multi space use this one
		//^(([gG][iI][rR] {0,}0[aA]{2})|((([a-pr-uwyzA-PR-UWYZ][a-hk-yA-HK-Y]?[0-9][0-9]?)|(([a-pr-uwyzA-PR-UWYZ][0-9][a-hjkstuwA-HJKSTUW])|([a-pr-uwyzA-PR-UWYZ][a-hk-yA-HK-Y][0-9][abehmnprv-yABEHMNPRV-Y]))) {0,}[0-9][abd-hjlnp-uw-zABD-HJLNP-UW-Z]{2}))$
		public PostcodeAttribute(): base(DataType.PostalCode)
		{
		}

		public override bool IsValid(object value)
		{
			if (value == null)
			{
				return true;
			}

			var valueAsString = value as string;
			return valueAsString != null && _regex.Match(valueAsString).Success;
		}

		public override string FormatErrorMessage(string name)
		{
			return string.Format("{0} is not a valid postcode", name);
		}
	}