Question

I am trying to query this very complicated XML document using xDocument and LINQ to XML. I want to perform the following action:

Get all elements that answer to a certain criteria, and if they don’t, return another attribute from the xDocument.

Example:

<cars>
    <car>
        <patrol type="oil">
            <url> http://Toyotaoil.com </url>
        </patrol>
    </car>
    <car>
        <patrol type="oil">
            <url> http://BMWoil.com </url>
        </patrol>
        <patrol type="gas">
            <url> http://BMWgas.com </url>
        </patrol>
    </car>
    <car>
        <patrol type="gas">
            <url> http://Hondagas.com </url>
        </patrol>
    </car>

Now what I’d like to get from this query is a list of patrols of type oil, unless the car doesn’t use petrol, and then I’d be satisfied with gas.

If I use the where clause I just miss the cases where the car uses gas. Is there any such thing like a where clause, where I can specify what to do if they condition wasn’t met?

Answer 1

The solution below should give you the flexibility to query whatever you like:

var result = from car in xdoc.Element("cars").Elements("car") 
             let patrols = car.Elements("patrol")
             let oils = patrols.Where(patrol => patrol.Attribute("type") == "oil")
             select new {
                    Car = car,
                    Patrols = (oils.Any() ? oils : patrols)
             }

I don’t have Visual Studio here, so I hope it compiles 🙂
Give a bit more information on what you like to select, and I’ll give you a more specific LINQ statement.