// usecase
class UseCaseX 
{
  private readonly UserCreator _userCreator;
  private readonly UserRoleAssigner _userRoleAssigner;

  public Task<ErrorOr<UserDto>> Execute(Input input) 
  {
    var trx = beginTransaction();
    var creationResult = await _userCreator.Create(new {...});
    if(creationResult.isError) 
      return ...

   var assignationResult = await _userRoleAssigner.Assign(creationResult.User.Id, [...roles...]);
   if(assignationResult.IsError) 
      return ...

   orm.saveChanges();
   trx.commit();
  }
}

// api handler
public async Task<IActionResult> CreateTemplate(
    [FromBody] CreateTemplateRequest request,
    [FromServices] IValidator<CreateTemplateRequest> validator,
    [FromServices] CreateTemplateUseCase useCase)
{
    if (Validate(validator, request)
        is { IsValid: false } failedModelState)
    {
        return ValidationProblem(failedModelState);
    }

    ErrorOr<TemplateDto> result = await useCase.Execute(new CreateTemplateData
    {
        CreateTemplate = ...transform request data...
    });

    if (result.IsError)
    {
        return new ErrorResult(result.FirstError);
    }

    return Json(new CreateTemplateResponse { Data = ...transform response data... });
}