I’m using C# with the System.Xml classes to manipulate an existing XML document.

In particular, I need to insert pieces of XML that I have in string form inside specific nodes in the document.

To do this, I create a new element and then set my XML string in its InnerXml property, like this:

using System.Xml;

string nsUri = "http://myorg/myns";
string baseDocument = @$"<?xml version=""1.0"" encoding=""utf-16""?><Root xmlns=""{nsUri}""></Root>";

XmlDocument doc = new XmlDocument();
doc.LoadXml(baseDocument);
var nsm = new XmlNamespaceManager(doc.NameTable);
nsm.AddNamespace("default", nsUri);

var target = doc.CreateElement("Target", nsUri);
target.InnerXml= @"
    <Sub1>This is a subnode</Sub1>
    <Sub2>Here is another subnode</Sub2>
";
doc.DocumentElement.AppendChild(target);

doc.Save(@"C:text.xml");

Looking at the output, here’s the result:

<?xml version="1.0" encoding="utf-16"?>
<Root xmlns="http://myorg/myns">
  <Target>
    <Sub1 xmlns="">This is a subnode</Sub1>
    <Sub2 xmlns="">Here is another subnode</Sub2>
</Target>
</Root>

As you can see, there’s an issue: every sub-node inside the XML string I inserted gets assigned an empty xmlns attribute: xmlns="".

This in itself is already a problem, but the far worse issue is that after doing this the document seems to be in an inconsistent state and further manipulation produces weird results. For example, if after doing this I do:

var sub1 = target.SelectSingleNode("default:Sub1", nsm);

then sub1 is null.

So, apparently this is not the correct way to do this, and the problem happens when I reassign InnerXml. Can you tell me the proper way to do this?

NOTE: I know I can create the elements and attributes one by one instead of just dumping the XML string inside InnerXml, but the XML fragments I need to insert are very long and it would be absurd to manually recreate them in code.