作为LINQ嵌套的foreach，带有链接的链表 [英] nested foreach as LINQ with chained linked List

问题描述

我在列表中有一个列表.我只需要列表中的一个值，就可以使用嵌套的foreach获得结果，但是我想使用某种LINQ查询.

I have a List within a list. I only need the one value from the list and can do obtain my result with a nested foreach but I want to use a LINQ query of some sort.

我的代码:

var myCity = from c in CountryLists
           select (from city in c.stateList
                   where city.name == passedInValue
                   select city.name).FirstorDefault();

这会返回myCity作为某种形式的列表，其中所有值都为null EXCEPT (找到匹配项的位置).

This returns myCity as a list of some sort with all values as null EXCEPT for where the match was found.

我不想遍历城市列表来查找名称.我如何在myCity中仅拥有一个价值；是null还是所需的名称?

i don't want to have to walk through the city list to find the name. How can I have only one value in myCity; either null or the desired name?

推荐答案

首先，使用SelectMany展平列表，然后使用FirstOrDefault进行过滤:

First, use SelectMany to flatten the list, then FirstOrDefault to filter:

CountryList.SelectMany(c => c.stateList).FirstOrDefault(d => d.Name == passedInValue);

请注意，由于FirstOrDefault可以使用谓词，因此实际上不需要Where子句.

Note that because FirstOrDefault can take a predicate, you don't actually need the Where clause.

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