public async Task <ICollection <Vacancy> > Search(int skip, int amount, VacancySearchModel searchModel, VacancySortModel sortModel)
{
IQueryable <Vacancy> vacancies;
vacancies = searchModel == null?vacancyRepository.ReadAll() : vacancyRepository.Find(searchModel);
var res = Sorting(vacancies, sortModel).Skip(skip).Take(amount);
var vacancyList = await Task.Run(() => res.ToList());
return(vacancyList);
}