c# - linq:单独的 orderby 和 thenby 语句

Question

我正在通过此处的 101 Linq 教程进行编码:

http://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b

大多数示例都很简单，但是这个让我大吃一惊:

    [Category("Ordering Operators")]
    [Description("The first query in this sample uses method syntax to call OrderBy and ThenBy with a custom comparer to " +
                 "sort first by word length and then by a case-insensitive sort of the words in an array. " +
                 "The second two queries show another way to perform the same task.")]
    public void Linq36()
    {
        string[] words = { "aPPLE", "AbAcUs", "bRaNcH", "BlUeBeRrY", "ClOvEr", "cHeRry", "b1" };

        var sortedWords =
            words.OrderBy(a => a.Length)
                 .ThenBy(a => a, new CaseInsensitiveComparer());

        // Another way. TODO is this use of ThenBy correct? It seems to work on this sample array.
        var sortedWords2 =
            from word in words
            orderby word.Length
            select word;

        var sortedWords3 = sortedWords2.ThenBy(a => a, new CaseInsensitiveComparer());

无论我使用哪种单词组合，长度始终是第一个排序标准......即使我不知道第二个语句(没有 orderby!)如何知道原始 orderby 子句是什么。

我要疯了吗？谁能解释 Linq 是如何“记住”原始顺序的？

Answer 1

OrderBy 的返回类型不是 IEnumerable<T> .这是IOrderedEnumerable<T> .这是一个“记住”所有给定顺序的对象，只要您不调用另一个方法将变量变回 IEnumerable。它将保留该知识。

请参阅 Jon Skeets 精彩的博客系列 Eduling，在其中他重新实现了 Linq-to-objects 以获取更多信息。 OrderBy 上的关键条目/ThenBy是:

• IOrderedEnumerable
• OrderBy, OrderByDescending, ThenBy, ThenByDescending