XML & LINQ: Reading Element Attribute Causing NullReferenceException

Question

I have a customers.xml file that looks like the following:

<?xml version="1.0"?>
<customers>
    <customer>
        <id>1</id>
        <name>Mike</name>
        <row test1="attribute1" test2="attribute2"/>
    </customer>
    <customer>
        <id>2</id>
        <name>John</name>
    </customer>
    <customer>
        <id>3</id>
        <row test1="attribute1"/>
    </customer>
</customers>

Some customers have the tag and others do not. When I try to store my xml data in an object I get a NullReferenceException on the tag where it is expecting a value but receives null for those customers that do not have the tag.

CustomerID = (string)e.Element("id"),
CustomerName = (string)e.Element("name"),
Test1Attribute = (string)e.Element("row").Attribute("test1"),
Test2Attribute = (string)e.Element("row").Attribute("test2"),

I thought by not using the .Value property and casting, that LINQ automatically resolves null values pertaining to the tag's attribute like it does for the element property.. What is the best case scenario to handle these null values for tag attributes? and can you explain why no similar errors are thrown for missing elements such as above (ex. customer 3) and likewise for missing attributes (ex. customer 3, test2). Thanks ahead of time!

Here are more details about the exception thrown:

System.NullReferenceException occurred HResult=0x80004003
Message=Object reference not set to an instance of an object.
Source=Test StackTrace: at Test.Program.<>c.b__2_2(XElement e) in C:\Test\Program.cs:line 89 at System.Linq.Enumerable.WhereSelectEnumerableIterator 2.MoveNext()
at System.Collections.Generic.List 1..ctor(IEnumerable 1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable 1 source) at Test.Program.Main(String[] args) in C:\Test\Program.cs:line 86

Yes I know, but how do I handle for those that do not have the element??? — useruseruser, Jun 12 '17 at 21:56
Simplest solution will be null-conditional operator `(string)e.Element("row")?.Attribute("test2")` — Sergey Berezovskiy, Jun 12 '17 at 21:57
Thank you. That solved my problem. I don't know if this should be considered a duplicate question. I am asking for solution to NullReferenceException specifically using XML & LINQ. I can rephrase questions if need be, but someone else could find this information useful. — useruseruser, Jun 12 '17 at 22:00
I agree with you and I would leave this question opened, but all questions about NullReferenceExceptions are usually closed as duplicates. Anyway, good to see that your problem is solved :) — Sergey Berezovskiy, Jun 12 '17 at 22:02
Very true. One more thing, what is the name of this syntax shortcut "?." Thanks again for your help! — useruseruser, Jun 12 '17 at 22:22
It's [null-conditional operator](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operators) — Sergey Berezovskiy, Jun 12 '17 at 22:23

XML & LINQ: Reading Element Attribute Causing NullReferenceException

0 Answers0