c# Linq to xml - 提取子元素的父元素

Question

I have this xml:

<Root>
  <RootKey>1</RootKey>
  <ChildL1>
    <ChildL1Key>12</ChildL1Key>
    <Child2>
      <Child2Key>TakeMe</Child2Key>
    </Child2>
    <Child2>
      <Child2Key>365</Child2Key>
    </Child2>
  </ChildL1>
  <ChildL1>
    <ChildL1Key>95</ChildL1Key>
    <Child2>
      <Child2Key>958</Child2Key>
    </Child2>
    <Child2>
      <Child2Key>574</Child2Key>
    </Child2>
  </ChildL1>
</Root>

I need to extract the the parents of the Child2 where Child2Key == "TakeMe". The result would be:

<Root>
  <RootKey>1</RootKey>
  <ChildL1>
    <ChildL1Key>12</ChildL1Key>
    <Child2>
      <Child2Key>TakeMe</Child2Key>
    </Child2>
  </ChildL1>
</Root>

I can probably do it in 2 steps. Iterate through parent upwards from Child2 and get their keys, and in the next step remove the elements with other keys. I'd rather do it in one query if possible.

Answer 1

XDocument xdoc = XDocument.Load(path_to_xml);
xdoc.Descendants("Child2")
    .Where(c2 => c2.Element("Child2Key").Value != "TakeMe")
    .Remove();

xdoc.Descendants("ChildL1")
    .Where(c1 => !c1.Descendants("Child2").Any())
    .Remove();

// now xdoc contains what you need
string xml = xdoc.ToString();

First query removes all Child2 nodes which does not match search condition.

Second query removes all ChildL1 which do not have Child2 nodes anymore.

Special for LB

xdoc.Descendants("ChildL1")            
    .Where(c1 => !c1.Descendants("Child2")
                    .Any(c2 => c2.Element("Child2Key").Value == "TakeMe"))
    .Concat(xdoc.Descendants("Child2")
                .Where(c2 => c2.Element("Child2Key").Value != "TakeMe"))
    .Remove();