Question

Trying to use a query like this:

var checkName = from nn in xdoc.Root.Elements("string")
                        where nn.Attribute("id").Value.Equals(newTag)
                        select thisbool = true;

To see if, in my XML, there exists a node string where the value of attribute id equals this string variable newTag. If there does NOT exist such a string node, I would like to return null, or something that I can check using an if statement directly below so that I may disallow a particular change to be made, i.e.

 if (thisbool)
        {
            MessageBox.Show("The string ID you entered is already in use. Please enter a different string ID.");
            tagBox.Text = undoTag;
            return;
        }

This is my current setup. I also tried just selecting nn and using if(nn != null) but nothing seems to work. I’m sorry if this is a newb question — I’m entering a bit of a time crunch, and I did indeed try to find an answer and test things out for 45min-1 hour.

Answer 1

This query will just all the elements that match your condition:

var checkName = from nn in xdoc.Root.Elements("string")
                        where nn.Attribute("id").Value.Equals(newTag)
                        select nn;

And then your if statement is as simple as checking if any such elements exist:

if (checkName.Any())
{
    // Code if condition is met by any tag here
}

If you really need a bool instead, you can combine the query like so:

bool anyMatches = xdoc.Root.Elements("string")
                   .Where(x => x.Attributes("id").Value.Equals(newTag)).Any();

Finally, for completeness sake, you can move the predicate from the Where() into Any():

bool anyMatches = xdoc.Root.Elements("string")
                       .Any(x => x.Attributes("id").Value.Equals(newTag));

I pesonally prefer one of the former two methods, since I think they spell out more clearly what’s going on. Up to you which you prefer, of course.