Check if any XML nodes exists with Specific Attribute using LINQ C#

Question

This is my XML:

<configuration>
    <Script name="Test Script">
        <arguments>
            <argument key="CheckStats" value="True" />
            <argument key="ReferenceTimepoint" value="SCREENING" />
            <argument key="outputResultSetName" value="ResultSet" />
        </arguments>
    </Script>
</configuration>

I am trying to use this linq statement to grab an argument element's value attrbiute if a specific key attribute exists.

XElement root = XElement.Load(configFileName);
var AttrVal = from el in root.Elements("Script").Elements("arguments").Elements("argument")
            where el.Attribute("key").Value == "CheckStats"
            select el.Attribute("value").Value;

Then I want to try and parse the attribute value into a boolean:

bool checkVal;
if (AttrVal != null)
{
    if (!bool.TryParse(AttrVal.First().ToString(), out checkVal))
    {
        throw new Exception(string.Format("Invalid value"));
    }
}

This code works if there is an element with that attribute, but if there isn't one, I get a System.InvalidOperationException: Sequence contains no elements.

How can I get around that? I thought by checking if (AttrVal != null) it would work. Should I replace that with if (AttrVal.FirstOrDefault() != null) or something similar? Thanks

have u tried if (AttrVal.FirstOrDefault() != null) by yourself before asking this question — BRAHIM Kamel
– BRAHIM Kamel, Commented May 9, 2014 at 14:42
You need to check that the attribute exists in your where before attempting to read its value - see: stackoverflow.com/a/2506840/61470 — user61470
– user61470, Commented May 9, 2014 at 14:51

qxg · Accepted Answer · 2014-05-09 14:56:09Z

1

In if statement, you can write

if (AttrVal != null && AttrVal.Any())

EDIT: I'm wrong. The exception should come from First(), not any of Elements(). Old answer:

from el in root.Descendants("argument")

Or

from el in root.XPathSelectElements("./Script/arguments/argument")

edited May 9, 2014 at 14:56

answered May 9, 2014 at 14:50

qxg

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3 Comments

Yuval Itzchakov Over a year ago

Does this answer your question?

RXC Over a year ago

I implemented the AttrVal.Any() check in the if statement and it looks like that was the part I was missing.

qxg Over a year ago

sorry. I updated my answer a few minutes before your comment.

BRAHIM Kamel · Accepted Answer · 2014-05-09 14:56:04Z

1

you have to check if there is already your attribute in the element where el.Attributes("key")!=null&&

XElement root = XElement.Load("config.xml");
            var AttrVal = from el in root.Elements("Script").Elements("arguments").Elements("argument")
                          where el.Attributes("key")!=null&&  el.Attribute("key").Value == "CheckStats"
                          select el.Attribute("value").Value;

            bool checkVal;
            if (AttrVal != null)
            {
                if (!bool.TryParse(AttrVal.First().ToString(), out checkVal))
                {
                    throw new Exception(string.Format("Invalid value"));
                }
            }

answered May 9, 2014 at 14:56

BRAHIM Kamel

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Comments

StuartLC · Accepted Answer · 2014-05-09 14:58:09Z

1

Here's a way to eliminate those pesky null checks - seek ahead with XPath to determine whether a node with both the necessary attributes (viz key="CheckStats" AND a value) exists, then parse it.

     bool checkVal;

     // using System.Xml.XPath;!
     var el = root.XPathSelectElement(
                    "/Script/arguments/argument[@key='CheckStats' and @value]");
     if (el != null && !bool.TryParse(el.Attribute("value").Value, 
         out checkVal))
     {
        throw new Exception(string.Format("Invalid value"));
     }

answered May 9, 2014 at 14:58

StuartLC

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