A big part of the Silverlight 4 release is the new WCF
RIA Services framework.
Its worth pointing out that WCF RIA Services doesn’t only target Silverlight clients – it also targetsAJAX
Common Silverlight application architecture looks something like this -
Between the two is “the gap” that has to be spanned by some kind of distributed application technology and there are various possibilities in Silverlight such as the following listed in the order in which they are layered on top of each other;
all of these technologies are “data transfer” technologies in that they move some bits from A to B.
It feels relevant to me to note that WCF offers a much higher level of abstraction than (say) raw socket programming in that you generally author services that are described in terms of a service contract and then offered over some binding that builds up the transport, encoding, security options and so on. On the client side you’re typically using metadata offered by the service in order to use tools to build up proxy classes to access the service.
It’s interesting how this combination comes together – with the right framework pieces and the right tools you can get to an abstraction that makes distributed programming far more productive.
On top of the WCF stack there’s also the WCF Data Services stack which offers OData compliant clients and services.
WCF Data Services is very data-centric in that you decide on that data that you want to expose and WCF Data Services exposes that for you in a RESTful manner as a number of AtomPub collections that you can then query into using OData’s URI syntax.
The services that you produce can be pretty much accessed from any platform and any client as you can see by taking a look at the consumers section on the OData website.
Whilst the focus is definitely on the data, WCF Data Services also makes it possible to expose arbitrary server-side operations as additional functionality and to intercept incoming operations and/or queries in order to add business logic but the primary intent is to expose data as the name of the technology suggests.
Silverlight is just one possible client for WCF Data Services and the client library does offer some higher level abilities than basic CRUD over entity sets with capabilities such as;
but the level of shared knowledge ( “coupling” ) between the client and the services is still very low.
Typically, the client developer adds a service reference to a WCF Data Service and the “shared knowledge” between the client and the service is downloaded in the form of the service metadata which describes to the client;
but that’s about the extent of it. There’s nothing shared about ( e.g. ) how to authenticate with the services, how authorisation might be performed by those services, how validation might be performed by the services etc.
There are upsides and downsides to this degree of separation – the potential for a variety of different clients and for independent versioning of the client/service are on the upside and productivity is a likely downside as you deal with the complexity of writing application logic on both the client and server side of the equation and code that shuffles collections of entities backwards and forwards whilst preserving state around whether they’ve been modified or not.
WCF RIA Services bridges “the gap” in a different, higher level way by embracing the idea that the client and the service are part of an application rather than separate clients and services that come together over an agreed contract.
Consequently, in a RIA Services application there is the tooling and framework support for sharing a richer set of artefacts between the client and the service than you’d see with a solution built around something lower level like a pure WCF solution allowing for a lot less friction in terms of;
I want to dig in to WCF RIA Services a little more over future posts but I thought for now it’d be good to start with a “magic demo” which illustrates the sort of speed that WCF RIA Services can give you when combined with Visual Studio 2010.
Its worth pointing out that WCF RIA Services doesn’t only target Silverlight clients – it also targets
Common Silverlight application architecture looks something like this -
Between the two is “the gap” that has to be spanned by some kind of distributed application technology and there are various possibilities in Silverlight such as the following listed in the order in which they are layered on top of each other;
- Sockets (
both TCP streaming and UDP multicast )
- HTTP ( via
the WebClient and HttpWebRequest classes )
- This might
be achieved by passing backwards and forwards XML and there are various
technologies in Silverlight to help with that such as LINQ to XML, XPath, XmlReaders/XmlWriters, XML
Serialization, WCF Data Contract Serialization
- Or you
might look to JSON and there are technologies in Silveright for dealing
with that such as the “LINQ to JSON” technology and/or the JSON
serialization technologies
- Windows
Communication Foundation ( WCF )
- Via HTTP
- Built-in
support doing text/binary encodings over HTTP(S)
- Built-in
support for authentication via transport mechanisms ( i.e. integrated
authentication via basic, digest or NTLM ) and via SOAP mechanisms (
i.e. “transport with message credential” )
- Via TCP
- Offering
the WCF duplex programming model for binary message transfer albeit
without security support
all of these technologies are “data transfer” technologies in that they move some bits from A to B.
It feels relevant to me to note that WCF offers a much higher level of abstraction than (say) raw socket programming in that you generally author services that are described in terms of a service contract and then offered over some binding that builds up the transport, encoding, security options and so on. On the client side you’re typically using metadata offered by the service in order to use tools to build up proxy classes to access the service.
It’s interesting how this combination comes together – with the right framework pieces and the right tools you can get to an abstraction that makes distributed programming far more productive.
On top of the WCF stack there’s also the WCF Data Services stack which offers OData compliant clients and services.
WCF Data Services is very data-centric in that you decide on that data that you want to expose and WCF Data Services exposes that for you in a RESTful manner as a number of AtomPub collections that you can then query into using OData’s URI syntax.
The services that you produce can be pretty much accessed from any platform and any client as you can see by taking a look at the consumers section on the OData website.
Whilst the focus is definitely on the data, WCF Data Services also makes it possible to expose arbitrary server-side operations as additional functionality and to intercept incoming operations and/or queries in order to add business logic but the primary intent is to expose data as the name of the technology suggests.
Silverlight is just one possible client for WCF Data Services and the client library does offer some higher level abilities than basic CRUD over entity sets with capabilities such as;
- ability to
turn LINQ formed queries into URI based syntax compatible with OData
- automatic
tracking of changes made to entities ( and entity sets ) returned from WCF
Data Services to make for automatic submission of changes
- ability to
deal with concurrent updates and the errors/retries that are needed to
deal with those situations
- batching of
queries/modifications to the server
but the level of shared knowledge ( “coupling” ) between the client and the services is still very low.
Typically, the client developer adds a service reference to a WCF Data Service and the “shared knowledge” between the client and the service is downloaded in the form of the service metadata which describes to the client;
- the “shape”
of the entities that the service exposes
- the entity
sets available
- the
relationship between entities such that those relationships can be
navigated
but that’s about the extent of it. There’s nothing shared about ( e.g. ) how to authenticate with the services, how authorisation might be performed by those services, how validation might be performed by the services etc.
There are upsides and downsides to this degree of separation – the potential for a variety of different clients and for independent versioning of the client/service are on the upside and productivity is a likely downside as you deal with the complexity of writing application logic on both the client and server side of the equation and code that shuffles collections of entities backwards and forwards whilst preserving state around whether they’ve been modified or not.
WCF RIA Services bridges “the gap” in a different, higher level way by embracing the idea that the client and the service are part of an application rather than separate clients and services that come together over an agreed contract.
Consequently, in a RIA Services application there is the tooling and framework support for sharing a richer set of artefacts between the client and the service than you’d see with a solution built around something lower level like a pure WCF solution allowing for a lot less friction in terms of;
- making the
service-side data model entities visible to the client side code
- offering
the ability for the client-side code to construct queries ( via LINQ )
which are then serialized, sent to the server for execution with the
result-sets then returned to the client including the ability to add
sorting, paging into those queries
- offering
automatic tracking of entity changes and entity-set changes on the client
side
- offering
easy mechanisms for submitting client-side changes back to the server side
and handling possible update failures
- offering
the ability to specify validation constraints and have them applied both
client- and service-side
- offering
the ability to share arbitrary code between the client and service
- offering
the ability to easily share ASP.NET services such as membership, roles,
profile with a Silverlight client
I want to dig in to WCF RIA Services a little more over future posts but I thought for now it’d be good to start with a “magic demo” which illustrates the sort of speed that WCF RIA Services can give you when combined with Visual Studio 2010.
