根据属性值返回一个元素 [英] Return an Element based on the value of an Attribute

问题描述

我有这个查询，但它似乎并没有执行我想要的操作.
我希望能够返回单个元素和子元素
基于属性ConfigName的值.

XML看起来像这样-

I''ve got this query but it doesn''t seem to do what I''d like.
I want to be able to return a single element and sub-elements
based on the value of attribute ConfigName.

XML looks like this -

<br />
<pre lang="xml"><Controllers><br />
  <PLC ConfigName="OP010"><br />
    <IPAddress>172.21.1.1</IPAddress><br />
    <SubnetMask>255.255.255.0</SubnetMask><br />
    <CommSlot>1</CommSlot><br />
    <CpuSlot>0</CpuSlot><br />
    <ProgName>OP010_ePRESS</ProgName><br />
    <CurveTag>Curve</CurveTag><br />
    <CommTimeOut>1000</CommTimeOut><br />
    <UpdateRate>250</UpdateRate><br />
  </PLC><br />
    <PLC ConfigName="OP020"><br />
    <IPAddress>172.21.1.2</IPAddress><br />
    <SubnetMask>255.255.254.0</SubnetMask><br />
    <CommSlot>1</CommSlot><br />
    <CpuSlot>0</CpuSlot><br />
    <ProgName>OP020_ePRESS</ProgName><br />
    <CurveTag>Curve</CurveTag><br />
    <CommTimeOut>1000</CommTimeOut><br />
    <UpdateRate>250</UpdateRate><br />
  </PLC><br />
br mode="hold" /></pre>

因此，如果我想查找OP010的数据，我希望它能正常工作，但由于它通过xmlElemList返回所有元素而没有出现-

So, if I want to find the data for OP010, I expected this to work, but it doesn''t appear to as it returns all of the elements via xmlElemList -

<br />
<pre lang="sql">var xmlElemList = from xmlElements in xmlTree.Elements("PLC")<br />
                  where (string) xmlElements.Attribute("ConfigName").Value == "OP010"<br />
                  select xmlElements;</pre><br />

有什么想法吗?我希望这返回一个元素.我可以运行查询，然后使用foreach获得想要的内容(如下所示)，但是看来我应该只能基于属性值返回想要的元素.

Any thoughts? I would like this to return a single element. I can run the query and then get what I want with a foreach (shown below), but it seems like I should be able to return only the element I want based on the attribute value.

foreach (var xmlElem in xmlElemList.OfType<XElement>())
{
  if ((string)xmlElem.FirstAttribute.Value == "OP010")
  {
    SelectedPLC.ConfigName = (string)xmlElem.FirstAttribute.Value;
    SelectedPLC.IPAddress = (string)xmlElem.Element("IPAddress");
    SelectedPLC.SubnetMask = (string)xmlElem.Element("SubnetMask");
    SelectedPLC.CommSlot = (Int32)xmlElem.Element("CommSlot");
    SelectedPLC.CpuSlot = (Int32)xmlElem.Element("CpuSlot");
    SelectedPLC.ProgName = (string)xmlElem.Element("ProgName");
    SelectedPLC.CurveTag = (string)xmlElem.Element("CurveTag");
    SelectedPLC.CommTimeOut = (Int32)xmlElem.Element("CommTimeOut");
    SelectedPLC.UpdateRate = (Int32)xmlElem.Element("UpdateRate");
  }

推荐答案

默认情况下，LINQ返回集合.如果您需要一次尝试单个 [singleOrDefault [ ^ ]，第一 [ FirstOrDefault [

by default LINQ returns collections. If you need a single try single [^], singleOrDefault [^], First[^] or FirstOrDefault[^] Methods

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