What is the difference between Linq to XML Descendants and Elements

I have came across both these ke开发者_如何转开发ywords in the VS IntelliSense. I tried to googling the difference between them and did not get a clear answer. Which one of these have the best performance with small to medium XML files. Thanks

Elements finds only those elements that are direct descendents, i.e. immediate children.

Descendants finds children at any level, i.e. children, grand-children, etc...

Here is an example demonstrating the difference:

<?xml version="1.0" encoding="utf-8" ?>
<foo>
    <bar>Test 1</bar>
    <baz>
        <bar>Test 2</bar>
    </baz>
    <bar>Test 3</bar>
</foo>

Code:

XDocument doc = XDocument.Load("input.xml");
XElement root = doc.Root;

foreach (XElement e in root.Elements("bar"))
{
    Console.WriteLine("Elements : " + e.Value);
}

foreach (XElement e in root.Descendants("bar"))
{
    Console.WriteLine("Descendants : " + e.Value);
}

Result:

Elements : Test 1
Elements : Test 3
Descendants : Test 1
Descendants : Test 2
Descendants : Test 3

If you know that the elements you want are immediate children then you will get better performance if you use Elements instead of Descendants.

Descendants will search the entire subtree of the current element for the specified name (or will return a flattened version of the tree if no name is provided), whereas Elements searches only the immediate children of the current element.