如何使用Linq比较两个XDocument之间的元素？

Question

I try to compare elements from two different XDocument's where some XElements match with each other in Linq and I also wanted to try out how you can show the elements in 'srcTree' that is not in 'srcTree2'. I tried before with a 'where' from Linq, but without any luck unfortunately.

My code below:

class LearnXML {
    static void Main() {
        XDocument srcTree = new XDocument(
            new XComment("This is a comment"),
            new XElement("Root",
                new XElement("Child", "data1"),
                new XElement("Child", "data2"),
                new XElement("Child", "data3"),
                new XElement("Child", "data4"),
                new XElement("Info", "info5"),
                new XElement("Info", "info6"),
                new XElement("Info", "info7"),
                new XElement("Info", "info8")
            )
        );

        XDocument srcTree2 = new XDocument(
            new XComment("This is a comment"),
            new XElement("Root",
                new XElement("Child", "data1"),
                new XElement("Child", "data4"),
                new XElement("Info", "info6"),
                new XElement("Info", "info8")
            )
        );

        Console.WriteLine(srcTree);

        XDocument doc = new XDocument(
            new XComment("This is a comment"),
            new XElement("Root",
                from el in srcTree2.Element("Root").Elements()
                join rp in srcTree.Element("Root").Elements()
                on !el.Element("Child").Value equals rp.Element("Child").Value
                select el
            )
        );

        Console.WriteLine(doc);
    }
}

Answer 1

Problem in your code is that you try to join two Roots by equality and then inverse it. So your code not even compile.

You can retrieve a difference between two Roots using a nested query. So the code below retrieve all differences nodes not only "Child" node.

      XDocument doc = new XDocument(
            new XComment("This is a comment"),
            new XElement("Root",
                from left in srcTree.Element("Root").Elements()
                where left != null && !(from right in srcTree2.Element("Root").Elements()
                                        where right != null
                                        select right.Value).Contains(left.Value)
                select left)
        );

If you really want to retrieve difference between nodes "Child" just get elements by name:

        XDocument doc = new XDocument(
            new XComment("This is a comment"),
            new XElement("Root",
                from left in srcTree.Element("Root").Elements("Child")
                where left != null && !(from right in srcTree2.Element("Root").Elements("Child")
                                        where right != null
                                        select right.Value).Contains(left.Value)
                select left)
        );