当结果为空时，LINQ会返回什么

小灰灰 2022-11-24 11:27 204阅读 0赞

本文翻译自：[What does LINQ return when the results are empty][]

*I have a question about LINQ query.* **我有一个关于LINQ查询的问题。** *Normally a query returns a `IEnumerable<T>` type.* **通常，查询返回`IEnumerable<T>`类型。** *If the return is empty, not sure if it is null or not.* **如果返回为空，则不确定它是否为null。** *I am not sure if the following `ToList()` will throw an exception or just a empty `List<string>` if nothing found in `IEnumerable` result?* **如果在`IEnumerable`结果中找不到任何内容，我不确定以下`ToList()`是否会抛出异常或只是一个空`List<string>` ？**

List<string> list = {"a"};
       // is the result null or something else?
       IEnumerable<string> ilist = from x in list where x == "ABC" select x;
       // Or directly to a list, exception thrown?
       List<string> list1 = (from x in list where x == "ABC" select x).ToList();

*I know it is a very simple question, but I don't have VS available for the time being.* **我知道这是一个非常简单的问题，但我暂时没有VS可用。**

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### \#1楼 ###

参考：[https://stackoom.com/question/504v/当结果为空时-LINQ会返回什么][https_stackoom.com_question_504v_-LINQ]

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### \#2楼 ###

*It will return an empty enumerable.* **它将返回一个空的可枚举。** *It wont be null.* **它不会是空的。** *You can sleep sound :)* **你可以睡觉:)**

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### \#3楼 ###

*.ToList returns an empty list.* **.ToList返回一个空列表。** *(same as new List() );* **（与新List（）相同）;**

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### \#4楼 ###

它不会抛出异常，你会得到一个空列表。

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### \#5楼 ###

var lst = new List<int>() { 1, 2, 3 };
    var ans = lst.Where( i => i > 3 );
    
    (ans == null).Dump();  // False
    (ans.Count() == 0 ).Dump();  // True

*(Dump is from [LinqPad][] )* **（转储来自[LinqPad][] ）**

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### \#6楼 ###

*Other posts here have made it clear that the result is an "empty" IQueryable, which ToList() will correctly change to be an empty list etc.* **这里的其他帖子已经明确表示结果是一个“空”IQueryable，ToList（）将正确地更改为空列表等。**

*Do be careful with some of the operators, as they will throw if you send them an empty enumerable.* **请注意一些操作符，因为如果向它们发送一个空的枚举，它们将抛出。** *This can happen when you chain them together.* **将它们链接在一起时会发生这种情况。**

[What does LINQ return when the results are empty]: https://oldbug.net/q/504v/What-does-LINQ-return-when-the-results-are-empty
[https_stackoom.com_question_504v_-LINQ]: https://stackoom.com/question/504v/%E5%BD%93%E7%BB%93%E6%9E%9C%E4%B8%BA%E7%A9%BA%E6%97%B6-LINQ%E4%BC%9A%E8%BF%94%E5%9B%9E%E4%BB%80%E4%B9%88
[LinqPad]: http://www.linqpad.net/