Question

I have a simple XML document that looks like this:

<Person>
  <LastName>LastName1</LastName>
  <FirstName>FirstName1</FirstName>
  <MiddleName>MiddleName1</MiddleName>
  <Suffix>Suffix1</Suffix>
</Person>

However I have a constraint where I am not allowed to add empty tags. Therefore if the Suffix value does not exist, I cannot use <Suffix /> or validation will fail.

I’m composing the XML structure using XElement objects from different classes that return their respective XML via a returned XElement object from a .ToXML() method. I need to check per element to see if the XElement being returned is null. If that’s the case it has to be like that line never existed. I’m trying to use the ?? operator but I’m getting the error that ?? left operand is never null. I had the code as follows:

public XElement ToXML()
{
  return new XElement("Employee",
    new XElement(this.LastName.ToXML()) ?? null,
    new XElement(this.FirstName.ToXML()) ?? null,
    new XElement(this.MiddleName.ToXML()) ?? null,
    new XElement(this.Suffix.ToXML()) ?? null);
}

How can I check per XML node to see if the XElement object being returned is null and if so ignore adding/composing that node all together? Any help is appreciated, thanks!

Answer 1

A constructor in C# will either return a non-null reference to the object or will throw an exception. It will not return null*.

As for your problem, why not:

return new XElement("Employee",
    this.LastName.ToXML(),
    this.FirstName.ToXML(),
    this.MiddleName.ToXML(),
    this.Suffix.ToXML());

And just have each of those ToXML methods return null if none exist?

Or if your case is the properties themselves are null:

return new XElement("Employee",
    this.LastName != null ? this.LastName.ToXML() : null, /* null is ignored */
    this.FirstName != null ? this.FirstName.ToXML() : null,
    this.MiddleName != null ? this.MiddleName.ToXML() : null,
    this.Suffix != null ? this.Suffix.ToXML() : null);

I also just realized perhaps you always get back an XElement, but it may be empty, in that case:

var elements = new[] { this.LastName.ToXML(), this.FirstName.ToXML(), ...

// use IsEmpty to filter out those that are <Element/>
return new XElement("Employee",
    elements.Where(ee => ee != null && !ee.IsEmpty));

_{*I believe there is an interesting edge case where you could get this from a COM interface instantiation, but we’ll ignore all “strange” coding.}