public async Task <ActionResult> OnPostUnregister(int?id, [FromServices] UserManager <User> userManager) { User = await userManager.GetUserAsync(HttpContext.User); CompetitionDto = _competitionService.GetCompetitions().Single(c => c.Id == id); _participationService.removeParticipation(id, User.Id); return(Redirect($"./Details?id=" + id)); }