MSDN Magazine - August 2008 - (Page 50)

that the Feed Reading View in Internet Explorer is turned off. This can be done from the Content tab of Tools | Internet Options. For all other data sources or to use additional database access technologies (such as LINQ to SQL), a mechanism is provided that enables any data source to be exposed as an ADO.NET Data Service using a plug-in model. In this case, URIs are converted into LINQ queries. Data Services enables this approach by mapping objects that implement the IQueryable interface to EntitySets. This means that ADO.NET Data Services is able to expose any data source that has an IQueryable provider written for it. In order to enable this, ADO.NET Data Services defines a mapping between CLR objects and artifacts of the EDM-based data model. Shortly, we will walk through the creation of an ADO.NET Data Service based on a simple CLR object graph. The steps we’ll illustrate produce a data service created over an in-memory collection of objects. In a typical production deployment, however, the IQueryable properties shown representing EntitySets would not expose in-memory data, but rather would translate IQueryable expression trees to data source-specific queries. For example, LINQ to Entities translates IQueryable expression trees into SQL statements. When creating a data service against a non-relational store, the data service is again created within an ASP.NET Web Application project. Note that this time, however, we skip the step used to create the ADO.NET Entity Data Model and begin by adding a new ADO.NET Data Service. The Add New Item wizard will generate a basic service, visible in the Solution Explorer. To continue with this simple example, we must now create the in-memory data that we plan to expose via our service. We do this by creating three classes, two of which are User and Contact, where each User will have a set of Contacts. The third class is a MyDataService class that exposes Figure 2 Creating In-Memory IQueryable Data Source public class User { public int ID { get; set; } public string Name { get; set; } public IList Contacts { get; set; } } public class Contact { public int ID { get; set; } public string Name { get; set; } public string Email { get; set; } } public class MyDataService { static User[] _users; static Contact[] _contacts; static MyDataService() { _users = new User[]{ new User{ID=1, Name="Mike"}, new User{ID=2, Name="Elisa"} }; _contacts = new Contact[]{ new Contact{ID=1, Name="Joe", Email="Joe@contoso.com"}, new Contact{ID=2, Name="Bob", Email="Bob@contoso.com"}, What about Non-Relational Data? two public properties (Contacts and Users) as IQueryable and IQueryable , as seen in Figure 2. Now that we have determined a data source, we return to familiar territory, changing the class definition to point to our data source, as seen here: public class contacts : DataService { public static void InitializeService(IDataServiceConfiguration config) { config.SetEntitySetAccessRule("*", EntitySetRights.All); } } Again, we must do some initial work to set security policy, since the initial service is locked down by default. The code shows the same security policy set at the EntitySet level, as we saw earlier. At this point, we again have a working ADO.NET Data Service that we can build and run. Testing the service can be accomplished by simply using Internet Explorer to browse to the service endpoint. Uniform URI Format The uniform Uniform Resource Identifier (URI) is one of the primary concepts that make up ADO.NET Data Services, which defines a relatively simple, yet expressive, URI format allowing applications to query for sets of entities or single entities, as well as traverse the relationships that exist between those entities. The structure of this URI enables agents and controls to understand easily how to navigate the data presented by a service. When we began testing our initial services, we saw the basic URI format pointing to the data service itself. Building on this basic URI, we are able to query the service using the following format, like so: http:// / / / [( ) [/ [( )/ ]]] For example, continuing with our earlier Northwind example, if we add /Customers to the end of the data service URI, / / new Contact{ID=3, Name="Sam", Email="Sam@contoso.com"}, new Contact{ID=4, Name="Carl", Email="Carl@contoso.com"}, new Contact{ID=5, Name="Abby", Email="Abby@contoso.com"}, new Contact{ID=6, Name="Annie", Email="Annie@contoso.com"}, }; _users[0].Contacts = new List (); _users[0].Contacts.Add(_contacts[0]); _users[0].Contacts.Add(_contacts[1]); _users[0].Contacts.Add(_contacts[4]); _users[1].Contacts = new List (); _users[1].Contacts.Add(_contacts[2]); _users[1].Contacts.Add(_contacts[3]); _users[1].Contacts.Add(_contacts[5]); } public IQueryable Users { get { return _users.AsQueryable ();} } public IQueryable Contacts { get { return _contacts.AsQueryable (); } } } 50 msdn magazine ADO.NET Data Services

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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