网上看到的：

class Program

    {

        static List<User> list = new List<User>()

        {

            new User(){ID=1,Name="Hello",Age=17,Hobby="a"},

            new User(){ID=2,Name="Boy",Age=50,Hobby="z"},

            new User(){ID=3,Name="Girl",Age=33,Hobby="x"},

            new User(){ID=4,Name="Fox",Age=43,Hobby="b"},

            new User(){ID=5,Name="Fire",Age=17,Hobby="f"},

        };

        static void Main(string[] args)

        {

            var q = list.AsQueryable().OrderBy("Name", true);

            q.ToList().ForEach(x => Console.WriteLine(string.Format("ID:{0},Name:{1},Age:{2},Hobby:{3}", x.ID, x.Name, x.Age, x.Hobby)));

            Console.ReadLine();

        }

    }

    public class User

    {

        public int ID { get; set; }

        public string Name { get; set; }

        public int Age { get; set; }

        public string Hobby { get; set; }

    }

//动态表达式

    public static class Test

    {

        public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string propertyName,

bool asc = true) where TEntity : class

        {

            string command = asc ? "OrderBy" : "OrderByDescending";

            var type = typeof(TEntity);

            var property = type.GetProperty(propertyName);

            var parameter = Expression.Parameter(type, "p");

            var propertyAccess = Expression.MakeMemberAccess(parameter, property);

            var orderByExpression = Expression.Lambda(propertyAccess, parameter);

            var resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExpression));

            return source.Provider.CreateQuery<TEntity>(resultExpression);

        }

    }