linq orderby通用类

public enum Sort
        {
            ASC,DESC
        }

        public static IQueryable<T> CreateSortQuery<T>(IQueryable<T> query, string field, Sort sort)
        {
            ParameterExpression param = Expression.Parameter(typeof(T), field);

            System.Reflection.PropertyInfo pi = typeof(T).GetProperty(field);
            Type[] types = new Type[2];
            types[0] = typeof(T);
            types[1] = pi.PropertyType;

            string sortwith;
            if (sort == Sort.DESC)
                sortwith = "OrderBy";
            else
                sortwith = "OrderByDescending";

            Expression exp = Expression.Call(typeof(Queryable), sortwith, types, query.Expression, Expression.Lambda(Expression.Property(param, field), param));
            return query.AsQueryable().Provider.CreateQuery<T>(exp);
        }