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Does a webservice is a standalone or can use outside classes

Can a web service use other classes that I have in a project or should it be standalone and use only it's own methods?
Thanks !

Does a web service can use other classes that I have in the project ?
YES it can. You can also return your custom class object, after serialization. Its very unusual that you would see webservice interacting with primitive types only (internally).

You can create instances of other classes and use them to perform work.
Any class in the same project or a referenced project should be usable, subject to the usual access modifiers.
You'll either need to include a using statement. Following example assumes you want to use SomeClass which resides in MyAssembly.SomeLibrary:-
using MyAssembly.SomeLibrary;
// in code block somewhere
var thing = new SomeClass();
or fully qualify the name of the class.
var thing = new MyAssembly.SomeLibrary.SomeClass();

It sounds like you are asking in terms of best practice rather than "is this technically possible". The answer depends on the class you want to use I suppose, but in general it is acceptable to use any other classes or libraries you want in a web service as this will not affect the client being able to consume the service (i.e. using LibraryA on the service side does not mean client 1 has to also have LibraryA installed to use your service).
It is possible to reuse those classes service side (in Visual Studio this is done by ticking the "Reuse types in referenced assemblies" box when you configure a service reference and then adding a reference to the appropriate project / dll), but I would generally advise against it as it can confuse matters - not all clients will have access to those dlls when consuming your service.

WCF ServiceKnownType design issue

I'm designing a new solution that will consist of three projects:
"Server" - a WCF service
"Client" - a winforms app that will call the WCF service
"ServiceContract" - a class lib containing some base classes plus the WCF service contract (interface). This will obviously be referenced by the Server, and also by the Client (I'm using a ChannelFactory rather than have VS generate a service reference). The service contract looks something like this:-
[ServiceContract]
[ServiceKnownType("GetCommandTypes", typeof(CommandTypesProvider))]
public interface INuService
{
[OperationContract]
bool ExecuteCommand(CommandBase command);
}
It's a very basic operation - the client creates a "command" object and sends it to the server to be executed. There will be many different commands, all inheriting from CommandBase (this base class resides in the "ServiceContract" project). As I'm using the base class in the WCF operation signature, I have to specify the known types which I'm doing dynamically using the ServiceKnownType attribute. This references a helper class (CommandTypesProvider) that returns all types deriving from CommandBase.
I've created a simple proof of concept with a couple of derived command classes that reside in the "ServiceContract" project. The helper class therefore only has to reflect types in the executing assembly. This all works fine.
Now in my "real" solution these command classes will be in different projects. These projects will reference the ServiceContract project, rather than vice-versa, which makes it difficult (or impossible?) for the helper to reflect the "command" assemblies. So my question is, how can I provide the known types?
Options I've thought about:-
The "Server" and "Client" projects will reference both the "ServiceContract" project and the various "command" projects. My helper could reflect through AppDomain.CurrentDomain.GetAssemblies(), but this fails because the "command" assemblies are not all loaded (I could force this by referencing a type in each, but that doesn't feel right - I want it to be a dynamic, pluggable architecture, and not have to modify code whenever I add a new command project).
Specify the known types in config. Again it would be nice if the app was dynamic, rather than have to update the config each time I add a command class.
Is there any way to access the underlying DataContractSerializer on both the client and server, and pass it the known types? I guess I'll still have the same issue of not being able to reflect the assemblies unless they've been loaded.
Refactor things to enable the ServiceContract project to reference the various command projects. I can then reflect them using 'Assembly.GetReferencedAssemblies()'. I guess the various command classes are part of the service contract, so perhaps this is the way to go? Edit: looks like this has the same problem of only finding loaded assemblies.
Any ideas greatly appreciated! Is it something that can be achieved or do I need to rethink my architecture?!
Thanks in advance.

One thing to consider is using the DataContractResolver.
Few resources:
WCF Extensibility – Data Contract Resolver by Carlos
Building Extensible WCF Service Interfaces With DataContractResolver by Kelly
Configuring Known Types Dynamically - Introducing the DataContractResolver by Youssef

Thanks for the replies regarding the Data Contract Resolver guys. I probably would have gone down this route normally but as I was using Windsor I was able to come up with a solution using this instead.
For anyone interested, I added a Windsor installer (IWindsorInstaller) to each of my "command" projects, which are run using Windsor's container.Install(FromAssembly.InDirectory.... These installs are responsible for registering any dependencies needed within that project, plus they also register all the command classes which my known types helper can resolve from the container.

Portable class library for shared [DataContract] class

This is probably a real simple one. I wished to create some code inside a [DataContract] class which is used to communicate information between a WCF service and consuming application.
I created a new Portable Class Library project and created inside it my [DataContract] class. It's really simple - it has a few easy attributes (strings mostly). I added a reference to the DLL in my WCF service and republished it. I then deleted the service reference from my consumer project and re-added it. It adds fine, no problems there.
The problem comes when I want to actually use it. See, the type is called 'Eval'. Some of the WCF methods return this 'Eval' type. So I have this serialized version of 'Eval' in the Reference.cs file within my service reference. Obviously this doesn't contain the method I'm looking for since it's just the serialized version. I can add the dll to the client project as well, but then I have two different Eval objects in two namespaces, and only the one from reference.cs is valid to be returned from the service calls.
So how do I ... erm... merge the two? So as the Eval objects that come back from the WCF service calls also have access to the method in question?
Thanks for reading, and stay safe on those roads.

When generating service reference you can specify what classes should be reused and what classes should be generated from service

Adding WCF Service References to multiple projects

A couple of very basic questions. I am new to WCF and I am building an application which has a Service Project, A Web Application project and a few Class library projects which I use for Business logic, etc.
I am hosting the WCF locally on my IIS and trying to add service references to the projects.
Question 1. When adding references, should I add a service reference to each project separately or is there a way I can share the same Service reference across the projects?
The reason I ask is because if I add separate references, each reference gets it own namespace, and when I have to pass the same object between the projects, I get an InvalidCastException because each ServiceClient has a different namespace.
Example -
Site.Business.XDataService.XDataServiceClient().GetItem()
is not the same as
Site.Web.XDataService.XDataServiceClient().GetItem()
Question 2. I specified the address of the local service in the class that implements the Service interface as below -
[ServiceBehavior(Namespace = "http://localhost:801/XDataService.svc", IncludeExceptionDetailInFaults = true)]
This doesn't seem right. If I move my code to a different/live environment, I would obviously have to change this part again and recompile. Where can I specify this (Web.Config?) so that I can change this address without having to rebuild my app?
Appreciate any kind of insight.
Thanks!

In answer to the first question, you can put the service reference in its own project and reference that project in all the other projects that need to access that service.
Basically all the service reference is is a lump of .NET code - namespace, class, etc.
Better yet (!) for a WCF service you also get an interface thrown in for free (more or less the same interface that you defined for your service) so you can do nice things in terms of dependency injection making testing etc easier.

First question - the service is just like any other code. For example, database access code. Should you put that in every project that needs to access your database? No - you should put it in a project which those other projects can reference.
As for your second question, you're specifying a namespace but I expect you think you're specifying a service endpoint address. The namespace is just like a C# code namespace - it essentially provides further identification and clarity in the event that you have multiple objects with the same name. Normally you'd use a namespace like http://mywebsite.com/MyService/VersionNumberIfRequired or similar.
The address itself is specified in configuration. The address will change depending on environment / deployment location - the namespace shouldn't.

Type Redefinition With WSE Web Service Import

Consider the following Visual Studio project structure
ProjectA.csproj
AClass.cs
ProjectB.csproj
References
ProjectA
Web References
AWebService
AWebService.csproj
References
ProjectA
ReturnAClassViaWebService.asmx
The issue occurs when ProjectB adds the web reference to AWebService and automatically generates all the proxy code for accessing AWebService including a new implementation of AClass. Since all of our other code needs to use the AClass defined in ProjectA, we're forced to convert the AWebService.AClass returned from the service into something we can use.
We're currently considering two solutions, neither of which are ideal.
Manually editing the generated Reference.cs to remove new definitions of AClass
Serializing AWebService.AClass to a stream then deserializing to ProjectA.AClass
Does anyone have any better solutions? This seems like something common enough for other developers to have experienced it.
Ideally we would like to have the proxy code generated in ProjectB to reference ProjectA.AClass rather than generating a whole new implementation.
Our environment is VS 2008 using .NET 2.0.

I have had the same problem that you are describing and I have tried both of the options you specify without being entirely happy about either of them.
The reason we both have this issue is at least partly because the shared-library-between-consumer-and-provider-of-a-web-service-solution is in violation of accepted patterns and practices for web service design. On the consumer side, it should be sufficient to know the interface published in the WSDL.
Still, if you are prepared to accept a tight coupling between your web service provider and web service consumer and you know for certain that your current client will never be replaced by a different client (which might not be capable of referencing the shared library), then I understand why the proposed solution seems like a neat way to structure your app. IMPORTANT NOTE: Can we really honestly answer yes to both of these questions? Probably not.
To recap:
The issue appears when you have classes (e.g. a strongly typed dataset) defined in some sort of shared library (used on both client and server).
Some of your shared classes are used in the interface defined by your web service.
When the web reference is added there are proxy classes defined (for your shared classes) within the web reference namespace.
Due to the different namespaces the proxy class and its actual counterpart in the shared library are incompatible.
Here are four solutions that can be tried if you want to go ahead with the shared library setup:
Don't. Use the proxy class on the client side. This is how it is intendend to be done. It works fine unless you simultaneously want to leverage aspects of the shared library that are not exposed by the web service WSDL.
Implement or use a provided copy/duplication feature of the class (e.g. you could try to Merge() one strongly typed dataset into another). A Cast is obviosuly not possible, and the copy option is usually not a very good solution either since it tends to have undesirable side-effects. E.g. When you Merge a dataset into another, all the rows in the target dataset will be labeled as 'changed'. This could be resurrected with AcceptChanges(), but what if a couple of the received rows were actually changed.
Serialize everything - except for elementary data types - into strings (and back again on the consumer side). Loss of type safety is one important weakness of this approach.
Remove the explicit declaration of the shared class in Reference.cs and strip the namespace from the shared class wherever it is mentioned within Reference.cs. This is probably the best option. You get what you really wanted. The shared class is returned by the web service. The only irritating drawback with this solution is that your modifications to the reference.cs file is lost whenever you update your web reference. Trust me: It can be seriously annoying.
Here is a link to a similar discussion:

You can reuse existing referenced types between the client and service by clicking on the 'Advanced' button on the 'Add Service Reference' form. Make sure the 'Reuse types in referenced assemblies' checkbox is checked and when the service client is generated it should reuse all types from project A.
In past versions this has not always worked correctly and I've had to explicitly select the shared type assemblies by selecting the 'Reuse types in specified referenced assemblies' option and then checking the appropriate assemblies in the list box. However, I just tested this with VS 2008 SP1 and it appears to work as expected. Obviously, you need to make sure that the types that are being used by the service and client projects are both from project A.
Hope that this helps.

We encountered a similar problem with one of our projects. Because we had several dependencies, we ended up creating a circular reference because project 1 required objects from project 2, but project 2 could not be build before project 3, which relied on project 1 to be build.
To solve this problem, we extracted all the public standalone classes from both projects and placed them inside a single librarie. In the end we created something like this:
Framework.Objects
Framework.Interface
Framework.Implementation
WebService
The WebService would be linked to all projects in our case, whereas external parties would only be linking to the objects and interface classes to work with. The actuall implementation was coupled at runtime through reflection.
Hope this helps