Oct 21 2010

…Something More about Ria Services

Data Validation 3: Silverlight, INotifyDataErrors, Ria Services and The Validation Toolkit for WPF & Silverlight

Silverlight…without Ria Services

In my previous post about data validation I spoke quite enough about Ria Services. I spoke about its kind of validation and how it is achieved, and also how to share classes among a Silverlight project and its hosting web site project (it is enough to put the share.cs or share.vb extension to a file on the server).

Discussing with people I discovered that there are a lot of  false beliefs about Ria services. For instance, a lot of developers think they can use Ria services only in conjunction with Entity Framework classes. This is simply false. Ria services allow you to define a context similar to the one of the EF entities also with general classes provided by the programmers: just follows the wizard that let you define your services…and will see it give you also this option.

If your classes are interconnected, you can benefit of Linq to Objects for your queries in a way completely analogous to EF objects.

With Ria services you can benefit of some pre-defined endpoints that have been adequately configured to fit well the needs of Silverlight users: you have a binary endpoint for intranet applications (its default), a soap endpoint for Internet applications and also a JSon endpoint. Moreover, you have also the option to expose OData (there is a check box in the wizard for the service definition). Instructions on how to define the endpoints in the configuration file are reported here. The bad news are that you cannot configure the features of the endpoints like in normal WCF services using the configuration file, but if you need features that are not contained in the standard configuration of the standard endpoints you have to define new endpoints in code.

Requiring a secure session is quite easy and can be done just by putting this attribute on the class that defines the service: [EnableClientAccess(RequiresSecureEndpoint = true)].Secure messages protocols are not supported by Silverlight. Don’t forget to give an https Url to a secured soap endpoint!

Requiring authentication and Role based authorizations are both easily achieved with attributes as explained here: http://msdn.microsoft.com/it-it/library/ee707361(en-us,VS.91).aspx. The above link explain also how to login and how to handle login errors.

Another, important thing that is worth to mention about Ria services concerns the return value of the Query methods of the service. According to the official documentation Query methods may return an IEnumerable<T>, an IQueryable<T> or a single object. However, what is not reported in the documentation is that only by returning an IQueryable one can  have an efficient filtering of data based on criteria passed by the Silverlight client to the server. For instance, suppose the Silverlight client needs to filter the customers returned by a Query method .GetCustomersQuery() defined on the server according to a user provided name. One can achieve this with the instruction:

 domainContext.Load(domainContext.GetCustomersQuery().Where(c => c.Name == "John").OrderBy(c => c.Age))

One could thing that all data returned by the server are then filtered by the Silverlight client. NO: behind the scene the Silverlight client build an IQueryable<T> and pass it to the server.Now, if also the server side method GetCustomerQuery() returns an IQueryable<T> the two queries are combined and either passed to the the Database or to Linq to Object to get the needed results efficiently! Therefore,  if you need to perform filtering based on client side defined criteria, please, always return an IQueryable<T>!

I thanks Gius that helped me clarifying well this point by speaking directly with a member of the WCF data services team.

Before concluding this short review post about Ria Services I would like to mention two more alternatives well suited for Silverlight clients: WCF Data Services, and WCF Rest Services. The WCF Rest Service Application template is not available in Visual Studio 2010 but it can be downloaded directly from Visual Studio 2010 by searching it in the Extension Manager(tool menu).

WCF Data Services are very similar to Ria services, The way you use it from Silverlight is quite the same. The main difference is that they don’t have any simple mechanism to share code with Silverlight and to handle validation. Moreover, you have to generate the proxy in Silverlight with Visual Studio and your context need to be specified by code(you need just to substitute a generic with an actual class…), and not with a simple wizard. The context may involve either EF entities or normal classes as in the case of Ria Services. This means some more job to be done but more flexibility because all things that Ria Services do in a standard way can now be customized! The only big loss is validation, but you can use my Validation Toolkit for WPF & Silverlight that is more flexible than the standard mechanism of Ria Services. However, it is important to mention that WCF Data Services just have one type of endpoint! The Rest endpoint! With a Rest endpoint queries are specified by adequately writing an URL, and the results are returned in the OData format that is a generalization of the Atom feed format. This means, you can send query not only with Silverlight but also with a simple browser! This is a very useful help in debugging the application. Obviously if you work with Silverlight all this details are hidden to you that just may use data contexts and IQueryables like with Ria Services.

WCF rest services use the same Rest protocol as the WCF Data Services but they are not connected to EF or classes, they are generic WCF services based on the Rest protocol. Parameters for the services are specified by the structure of the Url with the help of Routing tables defined in the Global.asax in a similar way to MVC Web applications. They are an interesting option to be considered for complex services that do more sophisticated computations than simply retrieving data from a Database.

Next post of this series will be again on validation, but on the server side…


                                                                                  Stay Tuned !


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CarlosAud CarlosAud Brazil says:

Thank you very useful