Question

Let’s say I am expecting XML as follows and I’m trying to pull the data in layer3:

<Layer1>
   <Layer2>
      <Layer3>Test</Layer3>
   </Layer2>
</Layer1>

C#:

var data = doc.Element("Layer1").Element("Layer2").Element("Layer3");

If the layer1 or layer2 elements are missing this will result in a null exception. I’m been wrapping these queries with try/catch and defaulting the variable in the catch block but this method smells. Is there a better way to set the “data” variable to null if any of the layers are missing?

Answer 1

var data = doc.Elements("Layer1").Elements("Layer2").Elements("Layer3").SingleOrDefault();

Note the use of Element*s*.

IEnumerable<T : XContainer>.Elements returns a collection of the child elements. The collection might be empty, but it won’t be null. Thus, you can chain Elements calls without fear of a NullReferenceException.

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As a side note, this is what VB does when you write

Dim data = doc.<Layer1>.<Layer2>.<Layer3>.SingleOrDefault()

(although in VB, you’d use the handy IEnumerable<XElements>.Value extension method instead of SingleOrDefault, which is, unfortunatley, unavailable in C#. Please leave a comment if you know of a C# equivalent.)