Using XMLreader and xpath in large xml-file C#

Question

So I have this rather large XML-file i need to parse and I don't want to load the whole file in memory. The XML looks something like this:

<root>
    <node attrib ="true">
        <child childattrib=1>
        </child>
    </node>
    <node attrib ="false">
        <child childattrib=1>
        </child>
    </node>
</root>

What I want to do is go through each node named node and see if the attribute matches my search-critera. And I want to do it using xpath. I found Parse xml in c# : combine xmlreader and linq to xml which helps me isolate the node in question. But I cant use xpath on the parent node. I guess I'll have to create an xmldocument and load the reader, but I cant get it to work the way I want to.

jdweng · Accepted Answer · 2017-08-22 17:11:48Z

2

Attributes need double quotes around value(childattrib). Try following which is a combination of xml reader and xml linq. When reading large xml files always use xmlreader.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;


namespace ConsoleApplication74
{
    class Program
    {
        const string FILENAME = @"c:\temp\test.xml";
        static void Main(string[] args)
        {
            XmlReader reader = XmlReader.Create(FILENAME);

            while (!reader.EOF)
            {
                if (reader.Name != "node")
                {
                    reader.ReadToFollowing("node");
                }
                if (!reader.EOF)
                {
                    XElement node = (XElement)XElement.ReadFrom(reader);
                    if ((Boolean)node.Attribute("attrib"))
                    {
                    }
                }
            }

        }

    }
}

edited Aug 22, 2017 at 17:11

answered Aug 22, 2017 at 16:07

jdweng

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3 Comments

LimuxKingen Over a year ago

So this is a great answer! Thank you! Now, can you point me in i direction where I via xpath can validate if the selected node has attribute = "true"? I tried : var xpathval = node.XPathSelectElement("node[@attrib='true']") but this doesn't return anything

Sach Over a year ago

@jdweng, regarding When reading large xml files always use xmlreader. Why is this so? I deal with XML files a fair bit in my line of work and would like to know the reason here. Thanks!

jdweng Over a year ago

Huge xml files will cause out of memory exceptions using other methods since the entire file is read into memory at one time.

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