Question

I load two XElements from two different files. One is a default file and the other is the live XML. Basically I need to know how to compare the two XElements and get a collection of all Elements that are in the live file and not in the defaultfile.

I don’t care about checking for values I only care if there is an element in the live file that isn’t in the default file.

Basically I am comparing two Web.config files and when a user is upgrading our product I need to check their web.config to find any element they have added that isn’t in our template and add them to our template before I lay it down and overwrite theirs.

Answer 1

Try this:

var addedNames = new HashSet<string>(
    liveXml.Elements().Select(e => e.Name).Except(
        defXml.Elements().Select(e => e.Name)
    )
);
var addedElements = liveXml
    .Elements()
    .Where(e => addedNames.Contains(e.Name))
    .ToList();

This approach constructs a list of liveXml‘s element names that are not present in defXml, puts them in a set, and then uses that set to filter liveXml‘s elements.

For removed elements, reverse the order of operand that you pass to Except, and filter defXml:

var droppedNames = new HashSet<string>(
    defXml.Elements().Select(e => e.Name).Except(
        liveXml.Elements().Select(e => e.Name)
    )
);
var droppedElements = defXml
    .Elements()
    .Where(e => addedNames.Contains(e.Name))
    .ToList();