c# linq xml attribute doesn't exist

Question

I am trying to read an xml file and get attribute but sometime this attribute doesn't exist.

When it doesn't exist, I get this error :

System.Linq.Enumerable+WhereSelectEnumerableIterator2[System.Xml.Linq.XElement,<>f__AnonymousType02[System.String,System.String]]

And :

Critical Error : System.NullReferenceException:....

My code :

string url = @"http://vigilance.meteofrance.com/data/NXFR33_LFPW_.xml";

XDocument doc = XDocument.Load(url);
var selectedBook = from r in doc.Descendants("DV")
                          .Where(r => (string)r.Attribute("dep").Value == Departement)
                           select new
                           {
                               Color = r.Attribute("coul").Value,
                               Risque = (string) r.Element("risque").Attribute("val").Value,
                           };

And the XML looks like this:

<DV dep="02" coul="1"/>
<DV dep="03" coul="3">
    <risque val="6"/>
</DV>

Does anyone have an idea ?

Charles Mager · Accepted Answer · 2016-07-18 18:38:21Z

1

The issue is that some DV elements don't have a child risque element, so in this part of your query:

Risque = (string) r.Element("risque").Attribute("val").Value

Element will return null, and you will get a null reference exception when you try to call Attribute.

You can fix this by making not going from sequence to single item until the end, and making use of the explicit conversions from elements and attributes to primitive types like string. This way, converting from attribute to string for a null attribute will just return null.

Risque = (string) r.Elements("risque").Attributes("val").SingleOrDefault()

See this fiddle for a working demo.

answered Jul 18, 2016 at 18:38

Charles Mager

26.3k2 gold badges41 silver badges52 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Hydro Over a year ago

Work great thank ! Do you know how to deal with multiple Risque node ? For example <DV dep="14" coul="2"><risque val="6"/><risque val="5"/> </DV>

Charles Mager Over a year ago

@Hydro it would depend on how you want to deal with it. Do you want the first? Last? Highest? Lowest? Total? A list of all of them?

Hydro Over a year ago

A list of all the risque value

Charles Mager Over a year ago

@Hydro in that case, use r.Elements("risque").Attributes("val").Select(x => x.Value).ToList().

jdweng · Accepted Answer · 2016-07-18 17:59:25Z

0

Try this

            XDocument doc = XDocument.Load(url);
            var selectedBook = doc.Descendants("DV")
                               .Where(r => (string)r.Attribute("dep") == Departement)
                               .Select(r => new {
                                   Color = r.Attribute("coul").Value,
                                   Risque = r.Element("risque") == null ? null : (string)r.Element("risque").Attribute("val").Value,
                               }).ToList();

answered Jul 18, 2016 at 17:59

jdweng

34.5k3 gold badges17 silver badges19 bronze badges

Collectives™ on Stack Overflow

c# linq xml attribute doesn't exist

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related