使用linq的OrderBy，如果明确知道是哪个字段，当然很容易：

 IQueryable<User> userQuery = ...; userQuery.OrderBy(u => u.Code)
   
   

    
    
1
    
    
2
   
   

但假如我们想写一个通用方法，预先并不知道要用哪个字段排序呢？

在网上寻寻觅觅，有许多国内的博客互相抄袭，信誓旦旦，但其实那些代码都运行不了。

还是老外的好使：
http://www.4byte.cn/question/33782/dynamic-orderby-using-linq-dynamic.html

我拿来修改了一下，可以用。主要思想是扩展Queryable。但里面的东西有许多我都看不懂。

    public static class QueryableExtension    {        public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> query, string propertyName)        {            return _OrderBy<T>(query, propertyName, false);        }        public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> query, string propertyName)        {            return _OrderBy<T>(query, propertyName, true);        }        static IOrderedQueryable<T> _OrderBy<T>(IQueryable<T> query, string propertyName,bool isDesc)        {            string methodname = (isDesc) ? "OrderByDescendingInternal" : "OrderByInternal";            var memberProp = typeof(T).GetProperty(propertyName);            var method = typeof(QueryableExtension).GetMethod(methodname)                                       .MakeGenericMethod(typeof(T), memberProp.PropertyType);            return (IOrderedQueryable<T>)method.Invoke(null, new object[] { query, memberProp });        }        public static IOrderedQueryable<T> OrderByInternal<T, TProp>(IQueryable<T> query, PropertyInfo memberProperty)        {//public            return query.OrderBy(_GetLamba<T, TProp>(memberProperty));        }        public static IOrderedQueryable<T> OrderByDescendingInternal<T, TProp>(IQueryable<T> query, PropertyInfo memberProperty)        {//public            return query.OrderByDescending(_GetLamba<T, TProp>(memberProperty));        }        static Expression<Func<T, TProp>> _GetLamba<T, TProp>(PropertyInfo memberProperty)        {            if (memberProperty.PropertyType != typeof(TProp)) throw new Exception();            var thisArg = Expression.Parameter(typeof(T));            var lamba = Expression.Lambda<Func<T, TProp>>(Expression.Property(thisArg, memberProperty), thisArg);            return lamba;        }    }
   
   

    
    
1
    
    
2
    
    
3
    
    
4
    
    
5
    
    
6
    
    
7
    
    
8
    
    
9
    
    
10
    
    
11
    
    
12
    
    
13
    
    
14
    
    
15
    
    
16
    
    
17
    
    
18
    
    
19
    
    
20
    
    
21
    
    
22
    
    
23
    
    
24
    
    
25
    
    
26
    
    
27
    
    
28
    
    
29
    
    
30
    
    
31
    
    
32
    
    
33
    
    
34
    
    
35
    
    
36
    
    
37
    
    
38
    
    
39
    
    
40
   
   

调用：

IQueryable<User> userQuery = ...;//正序userQuery = userQuery.OrderBy("Code");//降序userQuery = userQuery.OrderByDescending("Code");
   
   

    
    
1
    
    
2
    
    
3
    
    
4
    
    
5