How to build XmlNodes from XmlReader
Solution 1
The XmlNode
type does not have a public constructor, so you cannot create them on your own. You will need to have an XmlDocument
that you can use to create them:
XmlDocument doc = new XmlDocument();
while (xmlReader.Read())
{
//keep reading until we see my element
if (xmlReader.Name.Equals("myElementName") && (xmlReader.NodeType == XmlNodeType.Element))
{
// How do I get the Xml element from the reader here?
XmlNode myNode = doc.CreateNode(XmlNodeType.Element, xmlReader.Name, "");
nodeList.Add(myNode);
}
}
Solution 2
Why not just do the following?
XmlDocument doc = new XmlDocument();
XmlNode node = doc.ReadNode(reader);
Solution 3
XmlReader
and XmlDocument
have a very distinct way of processing. XmlReader
keeps nothing in memory and uses a forward-only approach as opposed to building a full DOM tree in memory for XmlDocument
. It is helpful when performance is an issue, but it also requires you to write your application differently: instead of using XmlNode
, you don't keep anything and only process "on the go": i.e., when an element passes by that you need, you do something. This is close to the SAX approach, but without the callback model.
The answer to "how to get the XmlElement" is: you'll have to build them from scratch based on the info from the reader. This, unfortunately, defies the performance gain. It is often better to prevent using DOM approaches altogether once you switch to XmlReader, unless for a few distinct cases.
Also, the "very handy" way to extract nodes using XPath (SelectNodes
is what you show above) cannot be used here: XPath requires a DOM tree. Consider this approach a filtering approach: you can add filters to the XmlReader and tell it to skip certain nodes or read until a certain node. This is extremely fast, but a different way of thinking.
Solution 4
Use XmlDocument.ReadNode
for this approach. Put XmlReader
in using statement and use XmlReader.LocalName
instead of Name to remove namespace prefix.
Solution 5
I've used the following workaround when I've had to insert data from a XmlReader
into a XmlDocumenht
:
XmlReader rdr = cmd.ExecuteXmlReader();
XmlDocument doc = new XmlDocument();
// create a container node for our resultset
XmlElement root = doc.CreateElement("QueryRoot");
doc.AppendChild(root);
StringBuilder xmlBody = new StringBuilder();
while(rdr.Read())
{
xmlBody.Append(rdr.ReadOuterXml());
}
root.InnerXml = xmlBody.ToString();
JohnIdol
The world will be mine but then I'll be killed by my own AI. Or by a giant simulated C. elegans out of the OpenWorm project. You can follow me on twitter.
Updated on July 09, 2022Comments
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JohnIdol almost 2 years
I am parsing a big number of big files and after profiling my bottleneck is:
XmlDocument doc = new XmlDocument(); doc.Load(filename);
This approach was very handy because I could extract nodes like this:
XmlNodeList nodeList = doc.SelectNodes("myXPath");
I am switching to XmlReader, but When I find the element I need to extract I am stuck with regards to how to build a XmlNode from it as not too familiar with XmlReader:
XmlReader xmlReader = XmlReader.Create(fileName); while (xmlReader.Read()) { //keep reading until we see my element if (xmlReader.Name.Equals("myElementName") && (xmlReader.NodeType == XmlNodeType.Element)) { // How do I get the Xml element from the reader here? } }
I'd like to be able to build a
List<XmlNode>
object. I am on .NET 2.0.Any help appreciated!
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JohnIdol over 14 yearsit seems to be creating empty nodes?
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Fredrik Mörk over 14 yearsYes, unless you add anything to the elements (by assigning something to the
InnerText
property for instance) they will be empty. -
JohnIdol over 14 yearsoh yep - looks obvious now since I am just passing element name in, thanks
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John Saunders about 14 yearsAlready answered. See stackoverflow.com/questions/1566192/….
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Karl Cassar about 10 yearsThis results in only empty nodes. You can use
doc.ReadNode(reader)
to actually get the entire node asXmlNode
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Karl Cassar about 10 yearsThis is the correct answer as the other one leaves blank nodes!