iterating XElements and then using XPath to extract child element values gets wrong value

Question

I have two methods:

• the first one parses a xml string into some XElements (where the xml is a sequence of 'banana' elements)
• the second one extracts the value from a child 'id' element and returns it

I have two alternative implementations of 'GetBananaId(XElement element)' - can anyone explain why the second 'wrong' implementation doesn't give the child element relative to its XElement parameter?

public void TestHarness()
{
    var xml = "<bananas><banana><id>A</id></banana><banana><id>B</id></banana><banana><id>C</id></banana></bananas>";
    foreach (var element in GetBananaElements(xml))
    {
        var right = GetBananaId(element);
        var wrong = GetBananaId_WRONG(element);
        Console.WriteLine("Right: {0}, Wrong: {1}", right, wrong);
    }
}

public IEnumerable<XElement> GetBananaElements(string recordsXml)
{
    var recordsXDoc = XDocument.Parse(recordsXml);
    return recordsXDoc.XPathSelectElements("//banana");
}

public string GetBananaId(XElement element)
{
    return element.Element("id").Value;
}

public string GetBananaId_WRONG(XElement element)
{
    return element.XPathSelectElement("//id").Value;
}

These produce the console output:

Right: A, Wrong: A
Right: B, Wrong: A
Right: C, Wrong: A

Answer 1

Use a relative path return element.XPathSelectElement("id").Value;, with //id you search down from / which is the document node.