The most efficient way to check for last element in XML

Question

Basically I just want to check if the last element in the XML document I have is called

<element99>

or not, and if so, read its attributes. What would be the most efficient way to do so?

Is there a way not to load entire XML doc into memory?

Answer 1

You could evaluate the XPath expression boolean(/*/*[last()]/self::element99) which returns true if the last element contained in the root element is named element99 . The expression /*/*[last()]/self::element99/@* returns the attributes of that element.

Answer 2

In XPath you could do (//*)[last()][self::element99]/@*

or you could do //element99[not(following::*)]/@* - but this isn't quite the same thing - it will match an element99 that has children, and depending what you mean by "last", an element with children is never the last element in the document.

Answer 3

You can use System.Xml.XmlReader . In this approach the file will be read element-by-element and will not be loaded fully in the memory.

The following method checks if an <element99> exists, and if it is the last element.

bool CheckXml(string path)
{
    XmlReader xmlReader = XmlReader.Create(new StreamReader(path));

    if (!xmlReader.ReadToFollowing("element99"))
        return false;

    if (xmlReader.NodeType != XmlNodeType.Element)
        return false;

    xmlReader.Skip();

    while (!xmlReader.EOF)
    {
        if (xmlReader.NodeType != XmlNodeType.EndElement && xmlReader.NodeType != XmlNodeType.Whitespace)
        {
            return false;
        }
        xmlReader.Read();
    }

    return true;
}

Since XmlReader only provides forward-only access, you have to

1. Read and store attributes before checking if the element is the last one.
2. Read the stream again and store the required attributes.