C# LINQ：如何将内部列表中的项目放入一个列表中？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/1028605/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
LINQ: How to get items from an inner list into one list?
提问by Stécy
Having the following classes (highly simplified):
具有以下类（高度简化）：
public class Child
{
public string Label;
public int CategoryNumber;
public int StorageId;
}
public class Parent
{
public string Label;
public List<Child> Children = new List<Child>();
}
And having the following data:
并有以下数据：
var parents = new List<Parent>();
var parent = new Parent() {Label="P1"};
parent.Children.Add(new Child() {Label="C1", CategoryNumber=1, StorageId=10});
parent.Children.Add(new Child() {Label="C2", CategoryNumber=2, StorageId=20});
parents.Add(parent);
parent = new Parent() {Label="P2"};
parent.Children.Add(new Child() {Label="C3", CategoryNumber=1, StorageId=10});
parent.Children.Add(new Child() {Label="C4", CategoryNumber=2, StorageId=30});
parents.Add(parent);
parent = new Parent() {Label="P3"};
parent.Children.Add(new Child() {Label="C5", CategoryNumber=3, StorageId=10});
parent.Children.Add(new Child() {Label="C6", CategoryNumber=2, StorageId=40});
parents.Add(parent);
Now, how would I get a list of children (with CategoryNumber=2) from the list of parents containing at least one child with CategoryNumber = 1 ?
现在，我如何从包含至少一个 CategoryNumber = 1 的孩子的父母列表中获取孩子的列表（CategoryNumber=2）？
I can do the following but it does not appear to be optimal:
我可以执行以下操作，但似乎不是最佳选择：
var validParents = from p in parents
where p.Children.Any (c => c.CategoryNumber==1)
select p;
var selectedChildren = validParents.Select(p => from c in p.Children
where c.CategoryNumber == 2
select c);
Here's what I get for selectedChildren:
这是我为 selectedChildren 得到的：
IEnumerable<IEnumerable<Child>>IEnumerable<Child>- C2 2 20
IEnumerable<Child>- C4 2 30
IEnumerable<IEnumerable<Child>>IEnumerable<Child>- C2 2 20
IEnumerable<Child>- C4 2 30
Is it possible to only have one flat list containing the two children elements instead of two sub-list? How would it translate in LINQ ?
是否可以只有一个包含两个子元素的平面列表而不是两个子列表？它如何在 LINQ 中翻译？
采纳答案by Eric Lippert
Scott's answer is great; I'd just like to point out that you can in fact do this query using query continuation syntax:
Scott的回答很棒；我只想指出，您实际上可以使用查询继续语法来执行此查询：
from parent in parents
where parent.Children.Any (c => c.CategoryNumber==1)
select parent into p
from child in p.Children
where child.CategoryNumber == 2
select child
Notice how the "into" lets you pipe the result of one query into the next query. Pretty slick, eh?
请注意“into”如何让您将一个查询的结果通过管道传输到下一个查询中。很圆滑吧？
回答by Scott Ivey
You can string a couple queries together, using SelectManyand Where.
您可以使用SelectMany和Where将几个查询串在一起。
var selectedChildren = (from p in parents
where p.Children.Any (c => c.CategoryNumber==1)
select p)
.SelectMany(p => p.Children)
.Where(c => c.CategoryNumber == 2);
// or...
var selectedChildren = parents
.Where(p => p.Children.Any(c => c.CategoryNumber == 1))
.SelectMany(p => p.Children)
.Where(c => c.CategoryNumber == 2);
