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c#xmlxpathxmldocument

XPath Expression with functions

I am trying to construct a XPath Expression to obtain the prices of all the albums, which were published at least 5 years ago. The XML document has the following structure:

<catalogue>
    <album>
        <year>1990</year>
        <price>7.99</price>
        ...
    </album>
</catalogue>

I tried with the following, but obviously, it has a problem:

string xPathExpression = "album[year<year-from-date(current-date())-5]/price";

This does not work either:

string xPathExpression = "album[year<year-from-date("2010-07-07")]/price";

It may be some namespace related issue or something. I found the following example, which I am not exactly sure how to implement on practice:

year-from-date(xs:date("2005-04-23"))

I am using C#, and more specifically XmlDocument(SelectNodes()).

Solution

  • year-from-date() and current-date() are XPath 2.0 functions. .NET's built-in XML libraries, including XmlDocument, only support XPath 1.0.

    In the case of year-from-date(), you can just use substring():

    album[year < substring("2010-07-07", 1, 4)]/price

    If you need a function that returns the current date, you can create a custom function resolver. This is a bit of a hassle to set up, but it will allow you to define XPath functions that do pretty much anything.