LINQ排序操作符包括：OrderBy、OrderByDescending、ThenBy、ThenByDescending及Reverse。
1. OrderBy
1>. 原型定义
public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector);
public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer);
2>. 示例
var products = from p in context.Products
orderby p.ProductID
select p;
IEnumerable<Product> products = context.Products.OrderBy(p => p.ProductID);
当扩展方法中有多个OrderBy操作符出现时，LINQ不会提示错误，将会以最后出现的OrderBy属性进行排序。
var products = context.Products
.OrderBy(p => p.ProductID)
.OrderBy(p => p.ProductName);
上面的例子中将按照ProductName进行升序排序。
2. OrderByDescending
1>. 原型定义
public static IOrderedQueryable<TSource> OrderByDescending<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector);
public static IOrderedQueryable<TSource> OrderByDescending<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer);
2>. 示例
var products = from p in context.Products
orderby p.ProductID descending
select p;
var products = context.Products.OrderByDescending(p => p.ProductID);
3. ThenBy
在使用ThenBy操作符之前，扩展方法表达式中必须有OrderBy或OrderByDescending。ThenBy可以多次出现，排序字段累加。
1>. 原型定义
public static IOrderedQueryable<TSource> ThenBy<TSource, TKey>(this IOrderedQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector);
public static IOrderedQueryable<TSource> ThenBy<TSource, TKey>(this IOrderedQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer);
2>. 示例
var products = from p in context.Products
orderby p.ProductID, p.ProductName
select p;
var products = context.Products
.OrderBy(p => p.ProductID)
.ThenBy(p => p.ProductName);
var products = context.Products
.OrderBy(p => p.ProductID)
.ThenBy(p => p.ProductName)
.ThenBy(p => p.UnitPrice);
4. ThenByDescending
1>. 原型定义
public static IOrderedQueryable<TSource> ThenByDescending<TSource, TKey>(this IOrderedQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector);
public static IOrderedQueryable<TSource> ThenByDescending<TSource, TKey>(this IOrderedQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer);
2>. 示例
var products = from p in context.Products
orderby p.ProductID, p.ProductName descending
select p;
var products = context.Products
.OrderBy(p => p.ProductID)
.ThenByDescending(p => p.ProductName)
.Select(p => p);
5. Reverse
1>.原型定义
public static IEnumerable<TSource> Reverse<TSource>(this IEnumerable<TSource> source);
2>. 示例
string[] weekdays = new string[] { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };
var expr = from weekday in weekdays
select weekday;
foreach (var item in expr.Reverse())
{
Console.WriteLine(item);
}