Lambda 动态表达式（排序）

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);
        }
    }