Professional LINQ phần 2

Cũng nhận thấy trong ví dụ trước đó dễ dàng hơn nhiều các mã được để đọc. Mã này thực sự theo cấu trúc của một tài liệu XML, vì vậy bạn có thể xem những gì các tài liệu XML kết quả sẽ như thế nào. Ví dụ tiếp theo sử dụng các loại XAttribute thêm một thuộc tính XML: | Chapter 1 Project LINQ Here are the results of this code Employee FirstName Scott FirstName LastName Klein LastName Employee You ll notice the use of var in the previous example. The var keyword tells the compiler to infer the type of the variable from the expression on the right side of the statement. The var keyword will be discussed in detail in Chapter 2 A Look at Visual Studio 2008 . Also notice in the previous example how much easier the code is to read. The code actually follows the structure of an XML document so you can see what the resulting XML document will look like. The next example uses the XAttribute type to add an attribute to the XML var x new XElement Employee new XAttribute EmployeeID 15 new XElement FirstName Scott new XElement LastName Klein var s - And here are the results from it Employee Employee 15 FirstName Scott FirstName LastName Klein LastName Employee While the capability to easily define the contents of the XML is cool the real power comes from the ability to pass an argument that is not user-defined but in reality comes from an outside source such as a query which can be enumerated and turned into XML via the standard query operators. For example the following takes the array of names from the first example and uses that as the source of the query for which to construct XML string firstnames Scott Steve Ken Joe John Alex Chuck Sarah var r new XElement Friends from fn in firstnames where S select new XElement Name fn rToString Here are the results from this code Friends Name Scott Name Name Steve Name Name Sarah Name Friends 13 Part I Introduction to Project LINQ This isn t to say that I only have friends whose first names begin with the letter S but you get the idea. This query returns a sequence of XElements containing the names of those whose first name begins with the letter S. The data comes not from a self-generated XML document but an outside source in this case the array of first names.