需要有关 XElement 查询的帮助

发布于 2024-10-01 11:22:43 字数 312 浏览 0 评论 0原文

此查询未按我的预期工作。有人看到问题了吗？

我试图通过名称获取元素，但它没有返回任何内容。以下是我需要帮助的函数的特定部分：

alt text

更新

解决方案是使用 XName 而不是字符串。就像这样：

var matchingElements = elements.Where(e => e.Name.Equals(XName.Get(name)));

原文

This query isn't working as I'm expecting it to. Anyone see the problem?

I'm trying to get an element by it's name, but it's not returning anything. Here is the specific part of the function I need some help with:

alt text

Update

The solution was to use an XName instead of a string. Like so:

var matchingElements = elements.Where(e => e.Name.Equals(XName.Get(name)));

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凌乱心跳 2024-10-08 11:22:43

尝试将您的行更改为：

elements.Where(e => e.Name.LocalName == name)

LocalName 部分是重要的部分，否则您将比较 XName 与 string 的相等性。请记住，XML 支持“前缀：元素名称”样式的名称。在该示例中，“prefix”是与 e.Name.Namespace 返回的命名空间关联的标识符，“element-name”是 e.Name.LocalName 返回的标识符>。

Try changing your line to:

elements.Where(e => e.Name.LocalName == name)

The LocalName part is the important part, as otherwise you are comparing equality of an XName with a string. Remember, XML supports names of the style "prefix:element-name". In that example, "prefix" is the identifier associated with the namespace returned by e.Name.Namespace and "element-name" is the identifier returned by e.Name.LocalName.

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孤独难免 2024-10-08 11:22:43

柯克的答案是正确的。我想指出您的代码的一些问题。

此行不必要地计算所有元素：

var hasMatch = matchingElements.Count() > 0;

您可以将其替换为 Any()，一旦找到元素，它将提前终止：

var hasMatch = matchingElements.Any();

接下来，验证 hasMatch 为 true 你应该调用 First() 而不是 FirstOrDefault() 因为你知道它此时必须有一个值。

话虽如此，您实际上可以按如下方式重写代码：

var matchingElement = elements.FirstOrDefault(e => e.Name.LocalName == name);
return (string)matchingElement;

这里转换为 string 将返回该元素的值（如果找到），否则将返回 null。使用强制转换只是为了防止它为 null，因为您将无法使用 matchingElement.Value，如果没有，则会抛出 NullReferenceException发现了元素。如果您希望只存在一个元素，您还应该考虑使用 SingleOrDefault。

Kirk's answer is right on the money. I wanted to point out a few issues with your code.

This line unnecessarily counts all the elements:

var hasMatch = matchingElements.Count() > 0;

You can replace it with Any() which will terminate early once an element is found:

var hasMatch = matchingElements.Any();

Next, having verified that hasMatch is true you should call First() instead of FirstOrDefault() since you know it has to have a value at that point.

Having said that, you could actually rewrite your code as follows:

var matchingElement = elements.FirstOrDefault(e => e.Name.LocalName == name);
return (string)matchingElement;

Here casting to a string will return the value of the element if it was found, otherwise it would return null. The cast is used just in case it was null since you wouldn't be able to use matchingElement.Value which would throw a NullReferenceException if no element was found. You should also consider using SingleOrDefault if you expect only one element to exist.

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