LINQ排序操作符包括：OrderBy、OrderByDescending、ThenBy、ThenByDescending及Reverse。

1. OrderBy

1>. 原型定義

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.Productsorderby p.ProductIDselect p; IEnumerable<Product> products = context.Products.OrderBy(p => p.ProductID);

　　當(dāng)擴(kuò)展方法中有多個OrderBy操作符出現(xiàn)時，LINQ不會提示錯誤，將會以最后出現(xiàn)的OrderBy屬性進(jìn)行排序。

var products = context.Products.OrderBy(p => p.ProductID).OrderBy(p => p.ProductName);

　　上面的例子中將按照ProductName進(jìn)行升序排序。

2.?OrderByDescending

1>. 原型定義

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.Productsorderby p.ProductID descendingselect p; var products = context.Products.OrderByDescending(p => p.ProductID);

3.?ThenBy

　　在使用ThenBy操作符之前，擴(kuò)展方法表達(dá)式中必須有OrderBy或OrderByDescending。ThenBy可以多次出現(xiàn)，排序字段累加。

1>. 原型定義

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.Productsorderby p.ProductID, p.ProductNameselect 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>. 原型定義

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.Productsorderby p.ProductID, p.ProductName descendingselect p; var products = context.Products.OrderBy(p => p.ProductID).ThenByDescending(p => p.ProductName).Select(p => p);

5. Reverse

1>.原型定義

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 weekdaysselect weekday;foreach (var item in expr.Reverse()) {Console.WriteLine(item); }

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