Refactor nested null checking for multiple possible string values

Question

I am parsing an XML file and trying to get the guid of a node where it has an attribute "name" and a value of "Name" like so:

<property name="Name" guid="7eca00b3-38e0-f0e8-9b72-2b822b21de6b" />
string propertyGuid = propertyList.Where(x => x.name == "Name").FirstOrDefault()?.ToString();
if (propertyGuid == (object)null) 
 throw new ArgumentNullException();

So I just found out that there are nodes that don't have a "Name" value but have a "Code" value. Which lets me check for another null value again

<property name="Code" guid="8bca00b3-38e0-f0e8-9b72-2b822b21de7a" />
string propertyGuid = propertyList.Where(x => x.name == "Name").FirstOrDefault()?.ToString();
if (propertyGuid == (object)null)
{
 propertyGuid = propertyList.Where(x => x.name == "Code").FirstOrDefault()?.ToString();
 if (propertyGuid == (object)null)
 throw new ArgumentNullException();
}

How do I refactor my code such that when another criteria (e.g "ID") is introduced in the future, I don't have to make another nested null check?

EDIT:

The check should be the other way around.

if ((object)propertyGuid == null)

• 404: null is null, no need to cast to an object
• t3chb0t: Is x your custom type with a name property because to me it looks a lot like pseudocode.
• jmc: @t3chb0t yes, it is generated from an XSD model
• jmc: @eurotrash edited the code, it should be the other way around if ((object)propertyGuid == null)

Answer 1

You can just go with :

// Just check both case at the same time
string propertyGuid = propertyList.Where(x => x.name == "Name" || x.name == "Code").FirstOrDefault()?.ToString();
if (string.IsNullOrEmpty(propertyGuid)) // Same check as you did but written differently
{ 
 throw new ArgumentNullException();
}

Then for the future, I guess that you can have Guids on node you don't want to extract. You could have properties on a list or array :

List<string> possibleName = new List<string>() {"Code", "Name"};

And then calling an extract function :

Public static string GetGuid(List<string> possibleName, Whatever propertyList)
{
 string propertyGuid = string.Empty;
 foreach (string name on possibleName)
 {
 propertyGuid = propertyList.Where(x => x.name == name).FirstOrDefault()?.ToString();
 if (!string.IsNullOrEmpty(propertyGuid)) 
 {
 return (propertyGuid);
 }
 }
 throw new ArgumentNullException();
}

Ps : I'd like to add that if propertyList is a NodeList you won't get what you want.

Answer 2

You can reduce some code and [IMO] increase readability with the following:

validPropertyValues should come from whatever source you want to manage this - database, config file, constant in code.

//valid values in the name property
var validPropertyValues = new List<string> { "Code", "Name" };
//check to see if name contains any of the accepted values
if (propertyList.Any(d => validPropertyValues.Contains(d.name)))
{
 //returns guid from the list. 
 //Using First() will throw an exception if guid doesn't exist
 //option 1
 //If guid will be populated if it exists
 return propertyList.Select(d => d.guid).First();
 //option 2
 //this version is only needed if guid can exist AND be empty
 var guidValue = propertyList.Select(d => d.guid).First();
 if (string.IsNullOrWhiteSpace(guidValue))
 {
 throw new ArgumentNullException();
 }
 return guidValue;
}