Dr. Dobb's Journal - February 2008 - (Page 28)

d02dino_p6ma 12/7/07 2:13 PM Page 28 Core Technology INSIDE VISUAL STUDIO 2008 (but not uniquely) in LINQ. In .NET, a delegate is an object-oriented wrapper for a function pointer and points to an existing and named function in a class. In .NET 2.0, managed languages offered new, powerful construct—anonymous methods. Basically, you have an explicit code snippet defined inline and used as an unnamed method of some class. Lambda expressions are a further refinement of the idea of an anonymous method, just less verbose and niftier. analogous keywords have in SQL. Translated to human language, the query assigns to the data variable all elements in the queryable object (a collection, in this case) that match the specified condition (all even numbers in this case). Here’s another LINQ expression that uses lambdas: var data = (from c in customers where c.Country == "USA" select c).SelectMany(c => c.Orders); inherits from a base class named DataContext. Visual Studio 2008 provides an ad hoc visual tool called “O/R designer”; see Figure 4. After you set up a database connection in the Server Explorer window, you drop tables and stored procedures in the designer and get a dynamically generated class to work with. Next, you simply instantiate this class and use it as the queryable object: NorthwindDataContext dataContext = new NorthwindDataContext(); var data = from c in dataContext.Customers where c.Country == "Spain" select c; LINQ Facilities Most Windows and web applications are centered on some sort of data repository, usually a relational database. To retrieve data, you have to use a different API each time. It can be SQL for relational databases, XQuery and XPath for XML documents, some interface (ICollection, for instance) for collections and arrays. The main goal of LINQ is unifying this model by providing an ad hoc framework. Conveniently, this query framework is wired to some new keywords in C# and VB: int[] fiboNumbers = new int[] {0,1,1,2,3,5,8,13,21,34}; var data = from n in fiboNumbers where n % 2 == 0 select n; As weird as it may seem, this is C# code that compiles in Visual Studio 2008. The new keywords are from, where, and select. Their meaning is really close to the meaning that A lambda expression is characterized by the => operator, prefixed by input parameters, and followed by the parametric expression to evaluate. The preceding code selects all U.S. customers and flattens the result set to a list of orders. Without the SelectMany keyword and the input lambda, you’ll get an array of collections of orders—not a list of order objects. LINQ operators work on objects that implement a particular interface— IQueryable. .NET 3.5 counts a number of these objects. They are wrappers for wellknown data containers such as collections, XML documents, DataSets, and SQL Server databases. The model is extensible too, so third-parties can provide their own LINQ engine to query Oracle databases or perhaps the filesystem. The most interesting of LINQ queryable objects is the object that wraps a SQL Server 200x database. It is a user-defined class that You can then go through the returned result set using a for/each statement or just bind the object to a data-bound control. Visual Studio 2008 Projects LINQ facilities span over all types of projects where database access and queries make sense. But other improvements are specific to web projects. For example, the editor of master pages has been enhanced to fully support nested master pages. Nested master pages were already working in ASP.NET 2.0, but were not fully backed by the visual designer of Visual Studio 2005. In addition, Visual Studio 2008 delivers support for split-view editing and a new CSS designer. A JavaScript debugger and IntelliSense extended to JavaScript classes complete the offering for web Figure 5: WPF designer in Visual Studio 2008. Figure 6: Workflow designer in Visual Studio 2008. 28 Dr. Dobb’s Journal l www.ddj.com l February 2008 http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - February 2008

Dr. Dobb's Journal - February 2008 Contents Hmmmm Alia Vox Developer Diaries Developer’s Notebook South American Software Development Conversations Inside Visual Studio 2008 BibPort: Creating Bibliographic References Continuous LINQ The ZK Framework Static Testing C++ Code The Agile Edge Effective Concurrency Swaine’s Flames

Dr. Dobb's Journal - February 2008

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