检查XML节点已与LINQ的C＃属性？ [英] Check if XML-node has attribute with Linq C#?

问题描述

我如何检查，看看如果一个节点实际上有一定的属性？我有一个包含多个节点看起来像这样的XML文件：

How can I check and see if a node actually has a certain attribute? I have an XML-file containing several nodes looking like this:

<Field From="OldString" To="NewString" /> 

到目前为止好。问题是，这种结构是即将被改变，一些节点将是这样的：

So far so good. The problem is that this structure is about to be changed to that some nodes will look like this:

<Field From="OldString" To="NewString" PrefixValue="OptionalAttribute" />

现在，当PrefixValue存在我应该在该属性的值在前面加上一个字符串，那是不是很困难，但我遇到了一些问题，当我尝试看看是否PrefixValue属性出现在所有的节点。在没有PrefixValue是本实例中，属性PrefixValue不会在节点处存在。我怎么会去检查，看看属性与LINQ的表达存在？

Now, when the PrefixValue is present I am supposed to prepend the value in that attribute to a string, and that is not very difficult, but I have run into some problems when I try to see if the PrefixValue attribute is present at all for a node. In the instances where no PrefixValue is present, the attribute PrefixValue will not exist in the node at all. How would I go about checking to see if the attribute exists with a Linq-expression?

推荐答案

你想要什么嘛，这取决于去做。如果你想在投影使用它，你可以使用：

Well, it depends what you want to do. If you want to use it in a projection, you can use:

(string) element.Attribute("PrefixValue")

这将返回null如果属性丢失，这是非常有用的。

That will return null if the attribute is missing, which is useful.

如果你想让它在where子句中，使用这样的：

If you want it in a where clause, use something like:

where element.Attribute("PrefixValue") != null

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