Looping through XML in .NET?

Question

I have some XML that looks something like the one below

<DriveLayout>
<Drive totalSpace="16" VolumeGroup="dg01" />
<Drive totalSpace="32" VolumeGroup="dg01" />
<Drive totalSpace="64" VolumeGroup="dg02" />
<Drive totalSpace="64" VolumeGroup="dg02" />
<VolumeGroups>
<VolumeGroup VolumeGroup="dg01" storageTier="1" />
<VolumeGroup VolumeGroup="dg02" storageTier="2" />
</VolumeGroups>
</DriveLayout>

I need a way to go back through the XML and add the attribute storageTier to each individual Drive node. Is there a way to loop through each drive node and grab the VolumeGroup then get the cooresponding storageTier out of the XML in the VolumeGroup node? I then need to inject the correct storageTier back into the XML drive node. I'm using the System.XML that's in C#.

Thanks

Any help would be greatly appreciated

Answer 1

I think you need XPath ( check this out )

var doc = new XmlDocument();
var xml =
    @"<DriveLayout>
<Drive totalSpace='16' VolumeGroup='dg01' />
<Drive totalSpace='32' VolumeGroup='dg01' />
<Drive totalSpace='64' VolumeGroup='dg02' />
<Drive totalSpace='64' VolumeGroup='dg02' />
<VolumeGroups>
<VolumeGroup VolumeGroup='dg01' storageTier='1' />
<VolumeGroup VolumeGroup='dg02' storageTier='2' />
</VolumeGroups>
</DriveLayout>
";

doc.LoadXml(xml);
var volumeGroups = doc.SelectNodes("/DriveLayout/VolumeGroups/VolumeGroup");
var storageTiers = new Dictionary<string, string>();
if (volumeGroups != null)
{
    foreach (var volumeGroup in volumeGroups)
    {
        var volumeGroupElement = (XmlElement) volumeGroup;
        storageTiers.Add(
            volumeGroupElement.Attributes["VolumeGroup"].Value,
            volumeGroupElement.Attributes["storageTier"].Value);
    }
}

var nodes = doc.SelectNodes("/DriveLayout/Drive");
if (nodes == null)
{
    return;
}

foreach (XmlNode node in nodes)
{
    var element = (XmlElement) node;
    var volumeGroupAttribute = element.Attributes["VolumeGroup"];
    if (volumeGroupAttribute == null)
    {
        continue;
    }

    var volumeGroup = volumeGroupAttribute.Value;

    var newStorageTier = doc.CreateAttribute("storageTier");
    newStorageTier.Value = storageTiers[volumeGroup];
    element.Attributes.Append(newStorageTier);
}

Answer 2

What was wrong with XSLT (Question on XPATH for an XSLT File And XSLT If Statement)?

Answer 3

This task can be done very succinctly using LINQ to XML. What is more, it uses simple LINQ queries and a dictionary to give an algorithm that runs in linear time.

var storageTiers = doc.Root.Element("VolumeGroups").Elements().ToDictionary(
    el => (string)el.Attribute("VolumeGroup"),
    el => (string)el.Attribute("storageTier"));
foreach (var driveElement in doc.Root.Elements("Drive"))
{
    driveElement.SetAttributeValue("storageTier", 
        storageTiers[(string)driveEl.Attribute("VolumeGroup")]);
}

If you are using C# 3.0, then this is without doubt the best way to go (unless your XML file is enormous and you need high efficiency, which seems unlikely).