I'm having very strange issue with my WCF Service Proxy client generated by "svcutil.exe" . My WCF Service works very fine if I don't have a function that returns DataTable. As soon as I add a method that returns a DataTable the client generated by svcutil.exe is behaving very strangely. The Interface is no longer found and client is not able to call the service. But if I add as a Service Reference its working very smoothly. I know its not a good habit to use DataTable as a return type but I need to. I cannot use the Service Reference :-( Any idea why its behaving or what I'm missing!!!
Have a look at the DataTableSurrogate class. It is used by the SyncFramework for serialization and really easy to use.
MSDN DataTableSurrogate
You shouldn't really serialize datasets, instead you should use datamodels and keep anything to do with datasets, tables, readers etc on your backend & in the business layer.
But.. if you want to do so you need to add the following "include" in svcutil, which is causing your issue. (Tells to reuse the types defined in System.Data.dll and not generate them in the proxy)
/r:C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\System.Data.dll
Related
Web service newbie... Please bear with me.
I was given a WSDL file to import into my vb .NET project. I understand that this is a contract which is supposed to tell me how to use the related web service. That's where my problem comes in. I see all kinds of classes, properties, Interfaces, etc. in the imported service reference. Nothing telling me that "if you have X, Y, and Z as inputs call this function to return W".
At the risk of sounding too vague, what is it that I should be looking for that tells me how I should be using this? How do I know which functions to call and from what classes to call them from? Should I expect some documentation to be provided with the WSDL or is the WSDL supposed to be enough for me to look at it and say "ahh, that's how this is used!".
I've read through the various WSDL tutorials out on the web and they gave me a basic understanding (I think...?). I'm missing something somewhere though and I'm really sure where.
Thank you for any assistance.
The classes that have been generated are easy to use.
Basically you would have one client class, and in that class one method for each endpoint/operation declared in the WSDL.
In addition, there should be one class for each complex type defined in the XSD part (the operation input arg object and output result object).
You can then invoke your WS in a way similar to the following (simplified) example.
Try
Dim service As New MyServiceRef.MyServiceClient()
service.Open()
Dim output As MyServiceRef.myCallResponse
Dim args As New MyServiceRef.myCallRequest
args.arg1 = 1
args.arg2 = "A"
output = service.myCallRequest(args)
...
Catch ex As Exception
treat ( ex )
End Try
The WSDL will tell you or, perferably, a SOAP library how to communitcate with the SOAP server. A SOAP service can be an interface to get data for almost anything.
However, if the function names and parameters are not named well, it could be very vague what data you are to send to the SOAP service and what the response will be.
Most of the time, it should be documented. You should get those documents or learn what the service actually does from the service provider. The WSDL is not really meant to be for human consumption. Though, if you are writing your own XML, then yes, you'd need to pay attention to the WSDL. If a library is creating the XML for you, it usually works with the WSDL to find out how to structure the XML and read the response.
When you add reference of the web service, it creates a proxy for you to call the web methods on the server. Here is a simple tutorial for consuming web services in VB.NET
As the title implies I am trying to get an understanding of why in WCF sometimes people choose to "generate proxies" vs using a ChannelFactory to manually create new channel instances. I have seen examples of each, but haven't really found any explanations of WHY you would go for one vs the other.
To be honest I have only ever worked with channels and the ChannelFactory<T> from code I have inherited, ie:
IChannelFactory<IDuplexSessionChannel> channelFactory =
binding.BuildChannelFactory<IDuplexSessionChannel>();
_duplexSessionChannel = channelFactory.CreateChannel(endpointAddress);
So why would I "generate a proxy"? What are the benefits and drawbacks?
The main difference is this:
generating a proxy only requires you to know the URL where the service resides. By generating the proxy, everything else (the service contract and the data contracts involved) will be determined by inspecting the metadata of the service
in order to directly create a ChannelFactory<T>, you must have direct access to the assembly that contains that service contract T for which you're generating a channel factory. This only ever works if you basically control both ends of the channel and you can share the assembly that contains those service contracts. Typically, with a third-party service, this won't be the case - with your own services, yes.
The second important point is this:
creating a generated proxy basically does the two steps that you would do - create a ChannelFactory<T>, and from that, create the actual channel - in a single constructor. You have no control over these two steps.
doing your own Channel creation is beneficial, since the creation of the ChannelFactory<T> is the expensive step - so yo could cache your channel factory instance somewhere. Creating and re-creating the actual channel from the factory is much less involved step which you can do more frequently
So if you do control both ends of the communication, service and client, you do have the option to share the service contracts in a separate assembly, and thus you have more options.
With most third-party services, you just simply don't have that option.
Using a proxy is simpler and easier to understand. You get to deal in terms of simple things - classes and methods on those classes - instead of complex, network-related things like channels.
OTOH, this is not made easier by the design flaw in WCF that prevents the same simple use of a WCF proxy that we could do with ASMX proxies:
using (var client = new MyServiceClient())
{
}
If you use this pattern with WCF, you can lose the original exception when the block is exited due to an exception. client.Dispose() can throw an exception, which will overwrite the exception originally being thrown. A more complex pattern is required.
This may help you:
When to use a proxy?
If you have a service that you know is going to be used by several applications or is generic enough to be used in several places, you’ll want to use the proxy classes.
When to use ChannelFactory?
ChannelFactory class is used to construct a channel between the client and the service without the need of a proxy. In some cases, you may have a service that is tightly bound to the client application. In such a case, you can reference the Interface DLL directly and use ChannelFactory to call your methods using that.
You could also refer following link to understand the difference between Channel Factory and Proxy class
http://ashishkhandelwal.arkutil.com/wcf/channelfactory-over-proxy-class-in-wcf/
The main advantage of the channelFactory is you can create the proxy at runtime dynamically on the fly. With SvcUtil (Add web reference in VS) you create the proxy at design time, so it's implementation is more static.
I am invoking a service through WCF and has encountered a problem with non-matching namespaces.
The object that is beeing sent though the service is in the namespace MyProject.Commons.BuisnessObjects, and I have verified this through WcfTestClient.
When I invoke a method clientside on the service (after initiated this with new MyServiceClient()), the method give me the correct objects, but with different namespaces.
The object is now of Web.MyService.Object. I have tried casting, but that didn't help.
Anyone who has seen this before?
Thanks, Tine
This is the expected behavior. It's how Web Services work. They are meant to be different types.
If you have added a service reference (i.e. WCF) rather than an old fashioned web reference, then you can match these up. Add a reference to the shared library defining your object type to the client before you add the service reference, then there is an option when you add the reference to re-use types.
This is because your types are not shared across service and client. Therefore the client does recreate for you your datastructures, in the Web.MyService namespace.
To avoid this you should share your data structure types between client and service by referencing your assembly containing your type BEFORE adding the service reference
You can find the detailed scenario and sample project there:
http://blog.walteralmeida.com/2010/08/wcf-tips-and-tricks-share-types-between-server-and-client.html
Just wondering under what circumstances would you prefer to generate a proxy from a WCF service when you can just invoke calls using the ChannelFactory?
This way you won't have to generate a proxy and worry about regenerating a proxy when the server is updated?
Thanks
There are 3 basic ways to create a WCF client:
Let Visual Studio generate your proxy. This auto generates code that connects to the service by reading the WSDL. If the service changes for any reason you have to regenerate it. The big advantage of this is that it is easy to set up - VS has a wizard and it's all automatic. The disadvantage is that you're relying on VS to do all the hard work for you, and so you lose control.
Use ChannelFactory with a known interface. This relies on you having local interfaces that describe the service (the service contract). The big advantage is that can manage change much more easily - you still have to recompile and fix changes, but now you're not regenerating code, you're referencing the new interfaces. Commonly this is used when you control both server and client as both can be much more easily mocked for unit testing. However the interfaces can be written for any service, even REST ones - take a look at this Twitter API.
Write your own proxy - this is fairly easy to do, especially for REST services, using the HttpClient or WebClient. This gives you the most fine grain control, but at the cost of lots of service API being in strings. For instance: var content = new HttpClient().Get("http://yoursite.com/resource/id").Content; - if the details of the API change you won't encounter an error until runtime.
Personally I've never liked option 1 - relying on the auto generated code is messy and loses too much control. Plus it often creates serialisation issues - I end up with two identical classes (one in the server code, one auto generated) which can be tided up but is a pain.
Option 2 should be perfect, but Channels are a little too limiting - for instance they completely lose the content of HTTP errors. That said having interfaces that describe the service is much easier to code with and maintain.
I use ChannelFactory along with MetadataResolver.Resolve method. Client configuration is a bother, so I get my ServiceEndpoint from the server.
When you use ChannelFactory(Of T), T is either the original contract that you can get from a reference in you project or a generated contract instance. In some projects, I generated the code from a Service Reference because I could not add a reference to the contract dll. You can even generate an asynch contract with the service reference and use that contract interface with ChannelFactory.
The main point of using ChannelFactory for me was to get rid of the WCF client config information. In the sample code below, you can see how to achieve a WCF client without config.
Dim fixedAddress = "net.tcp://server/service.svc/mex"
Dim availableBindings = MetadataResolver.Resolve(GetType(ContractAssembly.IContractName), New EndpointAddress(fixedAddress))
factoryService = New ChannelFactory(Of ContractAssembly.IContractName)(availableBindings(0))
accesService = factoryService.CreateChannel()
In my final project, the availableBindings are checked to use net.tcp or net.pipe if available. That way, I can use the best available binding for my needs. I only rely on the fact that a metadata endpoint exist on the server.
I hope this helps
BTW, this is done using .NET 3.5. However it does work also with 4.0.
Well in order to use ChannelFactory<T> you must be willing to share contract assemblies between the service and the client. If this is okay with you then ChannelFactory<T> can save you some time.
The proxy will build async functions for which is kind of nice.
My answer is a kind of summary of Keith's and Andrew Hare's answers.
If you do not control server, but have only WSDL/URL- generate proxy using Visual Studio or svcutil. (Note that Visual Studio sometimes failed, when svcutil works better).
When you control both server and client, share interfaces/contracts and call ChannelFactory
.
It's not just a matter of time saved. Using the WSDL generated proxy is dangerous because if you forget to update the service reference you can leave the solution in an inconsistent state. Everything compiles but the service contract is broken. I definetly suggest to use a ChannelFactory whenever possible, you make your life much easier.
A possible alternative could be to write a prebuild script that calls the SVCUtil utility to create the proxy everytime you build your project, but anyway ChannelFactory is much more neat and elegant.
Greetings!
I am using a WCF library on an application server, which is referenced by an IIS server (which is therefore the client). I would like to put my validation in a place so that I can just call .Validate() which returns a string array of errors (field too short, missing, etc). The problem is, such functions don't cross the WCF boundary and I really don't want to code the same logic in the WCF service and in IIS/WCF client. Is there a way to use extension methods or something similar so both side can use use a .Validat() method which calls the same code?
Many thanks for any ideas!
Steve
If you control both sides of the wire, i.e. the server-side (service) and the client-side, then you could do the following:
put all your service and data contracts into a shared assembly
reference that "Contracts" assembly from both the server and the client
manually create the client proxy (by deriving from ClientBase<T> or by creating it from a ChannelFactory<T>) - do not use "Add Service Reference" or svcutil.exe!
put all validation logic into a shared assembly
reference that shared validation assembly from both projects
If you want to use a shared validation assembly, you must make sure the data types used on your server and client are identical - this can only be accomplished if you also share service and data contracts. Unfortunately, that requires manual creation of the client proxy (which is really not a big deal!).
If you'd use "Add Service Reference", then Visual Studio will inspect the service based on its metadata, and create a new set of client-side objects, which look the same in terms of their fields and all, but they're a separate, distinct type, and thus you wouldn't be able to use your shared validation on both the server-side and the client-side objects.
Do you have a problem with sending the data over to the server to be validated? In other words, your service interface actually offers the "Validate" method and takes a data contract full of data, validates it and returns a List where T is some kind of custom ValidationResult data contract that contains all the info you need about validation warnings/errors.
In a service architecture, you can't trust the client, who could theoretically be some other company altogether, to have done proper data validation for you. You always need to do it at the service layer and design for communication of those validation issues back to your client. So if you're doing that work at the server anyway, why not open that logic up to the clients so they can use it directly? Certainly the clients can (should) still do some kind of basic input validation such as checking for null values, empty strings, values out of range, etc, but core business logic checks should be shipped off to the service.