Question

Ok I want my link query to return a list of users. Below is the XML

<section type="Users">
    <User type="WorkerProcessUser">
        <default property="UserName" value="Main"/>
        <default property="Password" value=""/>
        <default property="Description" value=""/>
        <default property="Group" value=""/>
    </User>
    <User type="AnonymousUser">
        <default property="UserName" value="Second"/>
        <default property="Password" value=""/>
        <default property="Description" value=""/>
        <default property="Group" value=""/>
    </User>
</section>

And my current LINQ Query that doesn’t work. doc is an XDocument

var users = (from iis in doc.Descendants("section")
                     where iis.Attribute("type").Value == "Users"
                     from user in iis.Elements("User")
                     from prop in user.Descendants("default")
                     select new 
                     {
                         Type = user.Attribute("type").Value, 
                         UserName = prop.Attribute("UserName").Value
                     });

I get an Object reference not set to an instance of an object exception. Can anyone tell me what I need to fix?

Here is my second attempt after fixing for the wrong property name. However this one does not seem to enumerate the UserName value for me when I try to use it or at least when I try to write it to the console. Also this returns 8 total results I should only have 2 results as I only have 2 users.

(from iis in doc.Descendants("section")
                     where iis.Attribute("type").Value == "Users"
                     from user in iis.Elements("User")
                     from prop in user.Descendants("default")
                     select new
                     {
                         Type = user.Attribute("type").Value,
                         UserName = (from name in prop.Attributes("property")
                                     where name.Value == "UserName"
                                     select name.NextAttribute.Value).ToString()
                     });

Answer 1

Your default elements don’t have a username attribute, username is a value of the property attribute.

And here’s how your query should probably look as an alternative to what Henk Holterman wrote. The difference being I selecting at the User element level rather than at the default[@property='UserName'] element level.

var usr = (from iis in doc.Descendants("section")
           where iis.Attribute("type").Value == "Users"
           from user in iis.Elements("User")
           select new
           {
               Type = user.Attribute("type").Value,
               UserName = (from prop in user.Descendants("default")
                           where prop.Attribute("property").Value == "UserName"
                           select prop.Attribute("value").Value).FirstOrDefault()
           });

Compared to your second attempt the code from prop in user.Descendants("default") has been moved into the anonymous type constructor and the assignment to UserName has been simplified.