Advanced Value Object Patterns in .NET

				
					// Assumption: URNs are case-insensitive
[ComplexValueObject(DefaultStringComparison = StringComparison.OrdinalIgnoreCase)]
// Enables serialization to/from a string "fileStore:urn".
[ObjectFactory<string>(UseForSerialization = SerializationFrameworks.All)]
public partial class FileUrn
{
   public string FileStore { get; }
   public string Urn { get; }

   // Validation and normalization of the file store and URN
   static partial void ValidateFactoryArguments(
      ref ValidationError? validationError,
      ref string fileStore,
      ref string urn)
   {
      if (string.IsNullOrWhiteSpace(fileStore))
      {
         validationError = new ValidationError("FileStore cannot be empty");
         return;
      }

      // Disallow colon because it is the separator used in serialization.
      // Alternatively, create a value object for FileStore and move the validation there,
      // or create a Smart Enum, if we have a fixed set of stores
      if (fileStore.Contains(':'))
      {
         validationError = new ValidationError("FileStore must not contain ':'");
         return;
      }
      
      if (string.IsNullOrWhiteSpace(urn))
      {
         validationError = new ValidationError("Urn cannot be empty");
         return;
      }

      // Normalize values
      fileStore = fileStore.Trim();
      urn = urn.Trim();
   }

   // Parsing/deserialization from string (required by [ObjectFactory<string>])
   public static ValidationError? Validate(
      string? value,
      IFormatProvider? provider,
      out FileUrn? item)
   {
      if (string.IsNullOrWhiteSpace(value))
      {
        item = null;
        return new ValidationError("FileUrn cannot empty");
      }

      var separatorIndex = value.IndexOf(':');

      // Basic format check: separator must exist and not be at the start or the end
      if (separatorIndex <= 0 || separatorIndex == value.Length - 1)
      {
         return new ValidationError("Invalid FileUrn format. Expected 'fileStore:urn'");
      }

      var fileStore = value[..separatorIndex];
      var urn = value[(separatorIndex + 1)..];

      // Delegate to the primary validation logic
      return Validate(fileStore, urn, out item);
   }

   // Serialization (required by UseForSerialization = SerializationFrameworks.All)
   public string ToValue()
   {
      return $"{FileStore}:{Urn}";
   }
}