private DbContext MyContext;

        public BaseRepository(DbContext context)

        {

            MyContext = context;

        }

public IQueryable<S> GetAllGroups<S>(Expression<Func<T, bool>> predicate, Expression<Func<T, S>> selectLambda)

        {

            var query = MyContext.Set<T>().Where(predicate).AsQueryable();

            return query.Select(selectLambda);

        }

List<Guid> lstguid=cis.GetAllGroups<Guid>(a => a.GroupID != null, a => a.GroupID).ToList();