public static class Paging
    {
        public interface ISortbyBuilder<TSource>
        {   
            IQueryable<TSource> SortBy(IQueryable<TSource> obj, LambdaExpression keySelector, bool asc);
        }public class SortbyBuilder<TSource, TKey> : ISortbyBuilder<TSource>
        {
            public IQueryable<TSource> SortBy(IQueryable<TSource> obj, LambdaExpression keySelector, bool asc)
            {
                var castedKeySelector = (Expression<Func<TSource, TKey>>) keySelector;
                return asc ? obj.OrderBy(castedKeySelector) : obj.OrderByDescending(castedKeySelector);
            }
        }public class SortbyBuilderCache<TSource>
        {
            private static readonly IDictionary<Type, ISortbyBuilder<TSource>> Cache = new Dictionary<Type, ISortbyBuilder<TSource>>();public static IQueryable<TSource> SortBy(IQueryable<TSource> obj, LambdaExpression keySelector, bool asc)
            {
                // TODO: I told you this is magic!
                var selectorReturnType = keySelector.Body.Type;
                ISortbyBuilder<TSource> sortbyBuilder;
                if (!Cache.TryGetValue(selectorReturnType, out sortbyBuilder))
                {
                    var typeArguments = new[] { typeof(TSource), selectorReturnType };
                    var builderType = typeof(SortbyBuilder<,>).MakeGenericType(typeArguments);
                    sortbyBuilder = (ISortbyBuilder<TSource>)Activator.CreateInstance(builderType);
                }
                return sortbyBuilder.SortBy(obj, keySelector, asc);
            }
        }public static IPagination<T> AsPagination<T>(this IQueryable<T> obj, int pageNumber, int pageSize, string sortExpression)
        {
            sortExpression = sortExpression ?? string.Empty;
            var asc = !sortExpression.Contains("DESC");

            var sortKey