MSDN Magazine - August 2008 - (Page 49)

Such services expose data using a uniform interface to be consumed by Web clients across a corporate intranet or the Internet. The framework consists of a server library to expose data securely as a service and a set of client libraries built for a range of Microsoft applications and technologies (the Microsoft® .NET Framework, Silverlight, and so on) to consume services. Figure 1 illustrates the architecture. rows and columns, a higher-level conceptual model is defined (as an Entity Data Model) over the relational data and the application is then programmed in terms of this model. The appliHTTP cation need only understand data in the shapes that make sense for the application and those Hosting /HTTP Listener shapes are expressed using a rich vocabulary Data Service Runtime that covers concepts such as inheritance, complex types, and explicit relationships. IQueryable [+ IUpdatable] In general, ADO.NET Data Services works Describing Data with the Entity by converting a request to perform an operation Data Access Layer Data Model over a resource (such as an HTTP request opCustom LINQ Entity Each ADO.NET Data Service is described in eration over a URI) to the equivalent operation Provider Framework Entity Data Model (EDM) terms using the Conon the data model that the resource represents. In this case, since the data model is backed by a ceptual Schema Definition Language (CSDL). The EDM uses two primary concepts, entities relational database, URIs are converted to Entity and associations (or relationships). Entities are Framework Object Services method calls. instances of Entity Types (such as Customer or An existing data model, created using the EnEmployee) which are structured records with tity Framework, can be exposed with only a few Relational Other Database Sources a key. An entity key is formed from a subset of steps in a Visual Studio® 2008 SP1 ASP.NET Web properties of the Entity Type. The key (CustomerApplication project. (Other project types and Id and OrderId, respectively) uniquely identifies Figure 1 The ADO.NET Data hosting mechanisms are also supported, such as and allows updates to entity instances and also Services Framework Architecture the Windows® Communication Foundation, or allows them to participate in relationships. Entities are grouped by WCF, WebServiceHost.) An ADO.NET Entity Data Model is first EntitySets (Customers is a set of Customer instances). Associations created or imported into an ASP.NET Web Application. With the form links between two or more Entity Types (such as Employee model available, we can then add a new ADO.NET Data Service. WorksFor Department). The Add New Item wizard will generate a basic service and make Why was the EDM chosen as the data description language for it visible in the Solution Explorer. We can then hook up the serADO.NET Data Services? As it turns out, the EDM maps very well vice to the model by changing the class definition, as shown here: using NorthwindModel; to the primary Web concepts of resources and links, making it an ideal candidate (entities for resources and associations for links). public class NorthwindService : DataService { The EDM was developed with the goal of becoming the core data public static void InitializeService(IDataServiceConfiguration config) model across a suite of developer and server technologies. With { only one data model to maintain across numerous applications, } application maintenance would be simplified. The EDM could be } used to define a model not only for custom applications built on Additionally, since the service is initially locked down by default, ADO.NET Data Services, but also as the input to reporting and visualization applications, intranet portal applications or work- we must do some work to set service-wide security policy to enflow applications. ADO.NET Data Services is the second Micro- able the service to be used. The following code sets security at the soft technology to build on the EDM concept (the first, of course, EntitySet level when the service is initialized: public static void InitializeService(IDataServiceConfiguration config) was the ADO.NET Entity Framework). For further information { on the EDM and the ADO.NET Entity Framework, see msdn.microconfig.SetEntitySetAccessRule("*", EntitySetRights.All); } soft.com/data and “ADO.NET: Achieve Flexible Data Modeling with the Entity Framework” in the July 2008 issue of MSDN® Magazine As you can see, this is a very simple example of setting security for at msdn.microsoft.com/magazine/700331. an ADO.NET Data Service. Other security methods and considerations will be discussed later. Relational Data At this point we have a working ADO.NET Data Service that By default, ADO.NET Data Services works closely with the we can build and run. ADO.NET Entity Framework to simplify the process of connectA simple way to test your service without a client app is to just ing to and exposing a data model over data stored in SQL Server® point a Web browser at the entry point of the service, for example or other third-party databases (Oracle, DB2, MySQL, to name / /service.svc. The entry point of the service will return merely a few). the response as XML containing the list of EntitySets exposed by The Entity Framework raises the level of abstraction at which de- the data service. To view Atom (the default format returned by an velopers work with data, meaning that rather than coding against ADO.NET Data Service) in Internet Explorer®, you must first ensure msdnmagazine.com August 2008 49 http://msdn.microsoft.com/data http://msdn.microsoft.com/data http://msdn.microsoft.com/magazine/700331 http://msdnmagazine.com

Table of Contents Feed for the Digital Edition of MSDN Magazine - August 2008

MSDN Magazine - August 2008 Toolbox CLR Inside Out Basic Instincts Cutting Edge Patterns in Practice Data 2.0 - Expose And Consume Data In A Web Services World Biztalk EDI - Build A Robust EDI Solution With BizTalk Server Silverlight - Create Animations With XAML And Expression Blend Write On! - Create Web Apps You Can Draw On With Silverlight 2 Wicked Code - Craft Custom Controls For Silverlight 2 Team System Foundations Windows With C++ Concurrent Affairs Going Places { End Bracket }

MSDN Magazine - August 2008

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