document.cs

abstract class DocumentXRequest {
  Optional<int> field1;
  Optional<string> fiedl2;

  DocumentXDomainModel validate();
}

class DocumentXCreateRequest: DocumentXRequest {
  DocumentXDomainModel validate() {
    // Validate create request
  }

  // Domain logic does not belong here
}

class DocumentXUpdateRequest: DocumentXCreateRequest {
  DocumentXDomainModel validate() {
    // Validate patch request
  }
  
  // Domain logic does not belong here
}

class DocumentXDomainModel {
  
}