C# Lambda && Linq

[TestClass] public class XmlLinqTest { private static XElement doc; [ClassInitialize] public static void Initialize(TestContext context) { doc = XElement.Load("Books.xml"); } [TestMethod] public void QueryBook_Id_ReturnBook() { IEnumerable<XElement> books=from el in doc.Elements() where el.Attribute("id").Value.Equals("1") select el; XElement book = books.First(); Assert.AreEqual(book.Attribute("id").Value, "1"); Assert.AreEqual(book.Attribute("name").Value,"Linq"); Assert.AreEqual(book.Attribute("author").Value,"Tom"); } }

<?xml version="1.0" encoding="utf-8" ?> 

<Books>

  <Book id="1" name="Linq" author="Tom" />

  <Book id="2" name="Lambda" author="Jerry" />  

</Books>

// custQuery     IEnumerable<IGrouping<string, Customer>>
// IGrouping group.. by       
var custQuery =

    from cust in customers

    group cust by cust.City into custGroup

    where custGroup.Count() > 2

    orderby custGroup.Key

    select custGroup;

<?xml version="1.0" encoding="utf-8" ?>

<Authors>

  <Author id="1" name="Tom" />

  <Author id="2" name="Jerry"/>

  <Author id="3" name="Jack"/>

</Authors>



<?xml version="1.0" encoding="utf-8" ?> 

<Books>

  <Book id="1" name="Linq" authorId="1" />

  <Book id="2" name="Lambda" authorId="2" />

  <Book id="3" name="C#" authorId="1" />

</Books>

var group = from author in authors.Elements()

                            join book in books.Elements() on author.Attribute("id").Value

                            equals book.Attribute("authorId").Value into BooksGroup

                            where author.Attribute("id").Value.Equals("1")

                            select new { Author = author.Attribute("name").Value, authorBooks = BooksGroup };

int[] numbers = { 5, 10, 8, 3, 6, 12}; //Query syntax:

        IEnumerable<int> numQuery1 = 

            from num in numbers where num % 2 == 0

            orderby num select num; //Method syntax:

        IEnumerable<int> numQuery2 = numbers.Where(num => num % 2 == 0).OrderBy(n => n);