I am going to develop the 3 tier application using Silverlight + WCF + ORM
Now my question is if I use ORM at database layer then how can I expose the classes at Presentation, Business layer to do Client-Side validation ?
If you used WCF RIA services instead of plain Silverlight WCF, you can attribute the properties of your data objects (in the associated metadata classes RIA creates for you).
This allows you to add basic validation rules, or even custom ones, that runs on both the server and client.
Using WCF RIA Services via a library is the preferred way to organise projects so try this link:
Walkthrough: Creating a RIA Services Class Library
Also:
Using WCF RIA Services
Creating Rich Business Applications using Silverlight 4 and WCF RIA Services
Various Channel 9 Videos
Is is generally a bad idea to expose your business entities directly to the frontend. Not only is what fits your backend layer rarely a good fit for your frontend but you also run the risk of exposing security critical information to the client - which should never be trusted.
An approach that generally worked well for us is developing the Silverlight Frontend using the MVVM pattern and have your WCF Service Layer return DTOs that can be more or less directly mapped to the data requirements of a ViewModel. This also satifies one of the most important rules when developing intranet/internet client server applications and that is to keep roundtrips to a mimimum because a DTO tailored to the needs of a particular viewmodel can include all the relevant information at once.
Related
I have a WCF service (using HTTP binding) that our WinForm and WFP apps can use with no problem. We have a Silverlight 4 developer who is saying he's not able to use the WCF service because it needs to be "reconfigured" for Silverlight use. I don't know if this is true or not, because I don't know anything about Silverlight.
So, my question is this. Should a WCF service, that uses HTTP binding, that is successfully being used by our WinForms and WPF applications, also be able to be consumed by Silverlight apps, without modifying or reconfiguring the WCF service?
Silverlight 4 supports the following bindings:
BasicHttpBinding
PollingDuplexHttpBinding
CustomBinding (with a subset of binding elements)
Silverlight and WCF Feature Comparison:
There are several ways to use the WCF
client stack to access a service.
It is used when invoking services
through automatically generated
proxies, as described in How to:
Access a Service from Silverlight. The
proxy must be generated in this
procedure by using the Add Service
Reference tool in Visual Studio 2010
for the Silverlight project.
Caution:
Proxies generated by using the WCF
Svcutil.exe tool will not work in
Silverlight 4. Use the SLsvcutil.exe
tool instead. For more information
about using this Silverlight tool, see
Using SLsvcUtil.exe to Access a
Service.
If you already have a Windows
Communication Foundation (WCF) service
contract definition, you can use the
generic ChannelFactory class without
having to generate a proxy. This might
be the case, for example, if your
client is sharing service definition
code with the project on the server.
In this case you could, for example,
define a service contract interface
IStockQuoteService and then use the
same IStockQuoteService code in both
the server and Silverlight projects.
This would involve using a
ChannelFactory.
This advanced technique is
demonstrated in How to: Call
Operations Asynchronously Using a
Channel Factory and in the Silverlight
4 context with Building and Accessing
Duplex Services. For more information
about defining and using service
contracts, see Designing Service
Contracts.
I am building a silverlight application using MVVM pattern but I don't understand what I am missing here...
ViewsProject (Silverlight Application) contains user controls and page. References ViewModelsProject.
ViewModelsProject (Silverlight class library) contains backend code of views. Also the business logic will reside in here. It will reference Models project.
ModelsProject (Windows class library) contains: Ado.net entity model of a local database and a WCF RIA DomainService built on the entity model. It's purpose is to get data from the local database and the entities are exposed via domain service.
Web project: Contains xap of ViewsProject.
Have I done everything correct so far? If yes then please help me understand:
How do I call the methods of the
domain service in the ViewsModel
project? If I reference the
ModelsProject, I get the error that
only silverlight projects can be
added.
If I change ModelsProject to a
silverlight class library project
then I can't add the entity model of
my database.
For client projects to use WCF RIA Service you need to set WCF RIA Services Link in project property.
As for modularity and separation in project architecture when using WCF RIA Services,
you can use WCF RIA Class libraries.
There isn't much sense in separating your views from your viewmodels IMHO. I've seen this approach used before but the view model (in my mind at least) represents a more 'view appropriate' abstraction of the data than the domain model can offer. The ViewModel provides a layer of indirection to allow the presentation to change without the model doing the same but it's little more than a sort of Adapter/Controller hybrid and lives alongside the view.
To answer your question though...
Typically, you'll have your SL project call your domain service (a web service usually) via commanding from your view to the viewmodel. The viewmodel command will then directly or indirectly make the web service call. This web service does not need to be a SL class library since it sits on the web server away from your client.
I get the feeling your thinking in terms of a desktop app here. Remember that the SL project runs client side and your data is not there. To wire all this up your gonna need some remote service to get the data from. A regular library reference is no good since the data is not on the client.
HTH, Stimul8d
I worked out the answer.
Change ViewModelsProject (Silverlight class library) to Silverlight Application type.
Check Enable Ria services during creation of the project.
In the view model class, add using ModelsProject.
Compile the ViewModelsProject.
All of the methods of the WCF Ria service will then appear in the code.
At the moment it seems that a RIA Domain Services class can not return a sinlge custom type.
There are parts of my app that needs just that, so think the only way to get that is to call back to a simple silverlight-enabled WCF Service, which i beleive will not have a problem returning a custom type. I don't see where the Silverlight client app has any sort of reference to the Ria Services. How do I set up both a Ria services and WCF service on the silverlight client. Will the WCF service be "aware" of the authenication already in place with the RIA services?
This is one of my biggest bugbears of RIA Services :). The good thing is that they are in the process of enabling complex types to be returned from invoke methods (according to the user voice site for RIA Services). However, that won't help you now :).
The best way to implement your requirement to return complex objects is indeed to set up a standard WCF Service to return complex types when required. You do so in the normal way that you would expose a WCF in any web project. You then consume it in your Silverlight application in much the same way you would a WCF Service in any other type of project (by adding it as a service reference). The main difference when consuming it (compared to other types of projects) is that Silverlight only supports asynchronous calls. One difference to be aware of from RIA Services is that whereas RIA Services automatically determines the URI of the domain services (based upon where the XAP file originated from), you will need to handle that aspect yourself (very important when you try to deploy your application :). Do this either by setting the URI in the app.config file, or use the method I use in the code accompanying this article here: http://www.silverlightshow.net/items/Building-a-Framework-for-Silverlight-Line-Of-Business-Applications.aspx.
In regards to your final question, yes, RIA Services uses standard ASP.NET authentication, so the cookie that it uses to maintain your authentication status is also used by any WCF Services in the same project. I talk a bit about security with WCF Services in this article if you want more information: http://www.silverlightshow.net/items/Building-a-Silverlight-Line-Of-Business-Application-Part-3.aspx.
Hope this helps...
Chris
Before reading, please know I've read all the other posts about the differences between vanilla WCF, WCF Data Services and RIA Services. My question is specifically about why RIA Services is being considered as a special kind of data source specifically for Silverlight when it seems to make more sense to just have it do one job: serve as a business logic layer behind a REST interface.
It looks like with the release of VS2010, RIA Services has solidified its stance as a business logic layer that sits behind a REST data access service - this seems to be confirmed by the new "Expose OData Endpoint" option on the Domain Service Class template in Visual Studio, which as far as I can tell essentially does for your RIA Service exactly what WCFDS does for an arbitrary data source (you could do this before, I believe, but the addition of this checkbox makes it clear that a RIA Service can be viewed as a layer containing business logic used to enhance a REST data endpoint and/or constraint it to a given set of queries, and not necessarily an endpoint in and of itself).
So, if I've got a RIA service with business logic, exposed via OData, I can add a reference to the OData service from a WCF client app. On the client, I get a DataServiceContext derivative that lets me do unit-of-work style work on the client. I can do the same thing from a Silverlight app and get what appears to be the same thing - a DataServiceContext derivative.
If I instead use a "RIA Service Link" in my Silverlight app to directly tie the app to the RIA service instead of adding a service reference, I get code generated by Visual Studio that appears to support pretty much the same patterns of work, but using a different style of API.
That being the case:
What are the advantages of a "RIA Services link," where a Silverlight app is tied directly to a RIA Service, as opposed to just adding a service ref to an OData endpoint that can be consumed by any kind of client without incurring tight coupling? I'm told that the magic of RIA is in the code generation, so I guess I'm trying to understand how the RIA code generation differs so much from "add service reference" code generation.
If there are advantages, why are these advantages made available specifically to Silverlight and not WCF client apps? Selling RIA services purely as a layer behind an OData endpoint seems like it would help standardize and push OData even further in terms of becoming a universal type of endpoint for any sort of client – “consume from ASP, consume from Silverlight, consume from WCF… you get virtually the same experience and it’s a great one.” Instead, we have Silverlight tied directly to RIA with a special set of functionality, and all other clients using the open protocol.
RIA services is not intended as "Domain logic behind oData" to the contrary and quite the opposite. The intention of RIA services is to abstract away the mechanics of web based data access to enable Rapid Application Development in Silverlight. Think of RIA
Services as to WCF as VB is to C++.
The key benefits of RIA Services are:
Transparent Data Access - there's no fiddling with svc files etc. You create an entity framework model, wrap it in a domain service and you're done. More importantly changes are propagated automagically. The developer doesn't have recreate the Service reference every time the model or a query changes, code gen does it for you.
Authentication framework out the box - It's there when you create a business app, it's a template in VS, a way to integrate with existing ASP.NET auth without having to do any heavy lifting.
Data Source Templates and Validation = Probably one of the most overlooked features but yet one of the most important. Have you opened the "data sources" window? RIA services creates User configurable DataContext bound Master/detail controls that support server side validation annotations. A functional data bound app is a drag and drop away. Consider the value of that to someone who is more Design/Blend focused.
In short RIA services is built for a developer to be able to go from an edmx data model to a secure functional Silverlight up in a matter of hours. It's awesome stuff when used in context.
As a note, I've done quite a bit of research on RIA Services and Data Services and they fulfill different needs. We use RIA Services for all our desktop replacement apps, but we use Data Services for SaaS.
I don't think you're far off with the long term intention of RIA services though. I think we'll see oData and RIA services get a lot closer in future versions.
The OData endpoint exposed by WCF RIA Services does not support query operations and returns data as-is. That means no benefit from IQueryable, sorting, parameters, etc. It will simply expose your methods; end of story. There is rumor that this will change in the next release however. However, what RIA Services provides from the standpoint of IQueryable on service calls, automatic propagation of business rules from the middle tier to the UI, and INotifyDataErrorInfo for flowing validation errors to the Silverlight client is outstanding should you choose to leverage them.
I am creating a Silverlight 3 application for which i am designing the security block. I already have an existent ASP.NET authentication module that i will reuse in the WCF security service(which will be like a wrapper and this will be called from Silverlight). My goal is to use SSL for the transport security. Also i would want this to be scalable as i don't want to query the DBMS for each authentication service call.
Any pointers on best design approaches.
Thank you. Anjan
If you already have it done in ASP.Net then you might want to take a look at .NET RIA Services. RIA Services allows you to hook into the ASP.Net authentication right inside of Silverlight. Brada has written about this and has a post on RIA Services Authentication here.