C# Linq to Xml：如果属性值等于 IEnumerable<XElement> 中的节点值，则选择元素
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/574432/
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 to Xml: selecting elements if an attribute value equals a node value in an IEnumerable<XElement>
提问by lolcat
I create an IEnumerable object that just contains the nodes I want from an xml file:
我创建了一个 IEnumerable 对象，它只包含我想要的 xml 文件中的节点：
IEnumerable<XElement> rosters = XDocument.Load("roster.xml")
.Elements("rosterlist")
.Elements("roster")
.Where(w => w.Element("division")
.Value
.Equals("SUPER AWESOME DIVISION"));
So it's a collection of these:
所以它是这些的集合：
<rosterlist>
<roster>
<userid>1</userid>
<name></name>
<etc></etc>
</roster>
<roster>
<userid>2</userid>
<name></name>
<etc></etc>
</roster>
</rosterlist>
I want to grab only the users where the useridattribute is also a useridnode within the rosterscollection.
我只想获取userid属性也是集合中userid节点的用户rosters。
IEnumerable<XElement> users = XDocument.Load("user.xml")
.Elements("userlist")
.Elements("user")
.Where(w => rosters.Elements("userid")
.Contains(w.Attribute("userid").Value));
But it is giving me an error:
但它给了我一个错误：
The type arguments for method 'System.Linq.Enumerable.Contains(System.Collections.Generic.IEnumerable, TSource)' cannot be inferred from the usage. Try specifying the type arguments explicitly.
无法从用法推断方法“System.Linq.Enumerable.Contains(System.Collections.Generic.IEnumerable, TSource)”的类型参数。尝试明确指定类型参数。
What is wrong with my approach?
我的方法有什么问题？
采纳答案by Gishu
One issue I see is that in the last code snippet, ...Elements("userid")returns a list of XElement objects which cannot contain a String returned by the Value property. This should work...
我看到的一个问题是，在最后一个代码片段中，...Elements("userid")返回一个 XElement 对象列表，其中不能包含 Value 属性返回的字符串。这应该工作...
IEnumerable<XElement> rosters = obRoot.Elements("rosterlist").Elements("roster");
var rosterUserIds = (rosters.Elements("userid").Select(r => r.Value));
IEnumerable<XElement> users = obRoot.Elements("userlist").Elements("user")
.Where(u => rosterUserIds.Contains(u.Attribute("userid").Value));
However I'd do this by using a join query.. Select user join rosters on userid
It'd go something like this
但是我会通过使用连接查询来做到这一点.. 在 userid 上选择用户加入名册
它会是这样的
string sXml = @"
<root>
<rosterlist>
<roster>
<userid>1</userid>
<name>R1</name>
<etc></etc>
</roster>
<roster>
<userid>2</userid>
<name>R2</name>
<etc></etc>
</roster>
</rosterlist>
<userlist>
<user userid='1'>
<name>User on roster</name>
</user>
<user userid='5'>
<name>User not on roster</name>
</user>
</userlist>
</root>
";
XElement obRoot = XElement.Parse( sXml );
var results = from user in obRoot.Elements("userlist").Elements("user")
join roster in obRoot.Elements("rosterlist").Elements("roster")
on user.Attribute("userid").Value equals roster.Element("userid").Value
select new {Name=user.Element("name").Value, RosterName=roster.Element("name").Value} ;
foreach (var v in results)
{
Console.WriteLine("{0, -20} on Roster {1, -20}", v.Name, v.RosterName);
}
Outputs:
输出：
User on roster on Roster R1
