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