private IQueryable <Country> FilterCountries(IQueryable <Country> query, CountryFilter filter)
        {
            if (filter != null)
            {
                query = filter.FilterCountries(query);
            }

            return(query);
        }
 public async Task <IEnumerable <Country> > GetAllWithFilter(CountryFilter filter)
 {
     return(await FilterCountries(db.Countries, filter)
            .OrderBy(c => c.Name)
            .ToListAsync());
 }