Question about web services and sharing classes

[Chris Dunaway]

How can a class be shared between a web service and a client that consumes
the web service?

Suppose I have a Class Libraray with the following simple class:

Public Class SimpleClass
Private _AnInteger As Integer

Public Property AnInteger As Integer
Get
Return _AnInteger
End Get
Set(ByVal Value As Integer)
_AnInteger = Value
End Set
End Property
End Class

This is compiled to a .DLL.

Now, I create a Web Service project and Reference the ClassLibrary and then
add a Web Method as follows:

<WebMethod()> _
Public Sub DoSomething(ByVal sc As SimpleClass)
'Do Something with sc here
End Sub


Finally, I create a Windows Forms Application to consume the web service.
I add the Web Reference to the web service and also Reference the
SimpleClass library and everything looks OK so far, until I try to use
them. Here is an example

Private Sub Button1_Click(...) Handles Button1.Click
'Declare an instance of the web service
Dim ws As New localhost.Service1

'Create an instance of the simple class
Dim sc As New SimpleClass

'Now call the web service method:
ws.DoSomething(sc) '<------- Error here
End Sub

When I try this, it tells me that it cant convert an instance of
SimpleClass to localhost.SimpleClass.

If I change the instantiation of the simple class as follows:

Dim sc As New localhost.SimpleClass

Then it seems to work OK. But my problem is that if SimpleClass in the
ClassLibrary has methods and not just properties, those methods are not
available in the localhost.SimpleClass version, just the properties.

Is it possible to share a ClassLibrary in this manner?

Any assistance would be appreciated.

Chris

 

[Malek]

Your code didn't work, not because your class cannot be shared between the
server and client, but because the proxy has declared the method argument as
being localhost.SimpleClass ... arrange your proxy class, and it will do
fine ...

However, you are defeating the whole idea behind web services when you want
to have the class shared ... You are totally in an RPC mind set, why then
use a message oriented technology and architecture ? Do you really mean to
do your class sharing outside of your own context (with partners and such)?
why ? if it is more like an intranet setting, Enterprise Services stays your
best choice, most performing, most secure and richest features ... if it is
a problem with going through firewalls and such (although I don't see why
you would really need RPC outside of firewalls, if you think a little about
it) why not go for remoting (it can use http, it can go through firewalls
....etc. Well, I have lots of reasons for not recommending it, but still, if
you need RPC so badly across firewalls...).
If it is about interop, then class sharing is totally out of question ...

 

[Rick Strahl [MVP]]

Hi Chris,

No you can't do this unfortunately with standard Web Services. I've also
often wanted to do this because I have many application where the same
business objects sit both on the client and the server. It seems logicial
that you should be able to pass an object from client to server, but the
plain WebService architecture MS has doesn't work that way.

As Malek pointed out Web Services work of Proxy objects which are actually
very different than the 'live' object that is passed back from the server.
For one thing it has a completely different structure as methods aren't
proxied.

SO your workaround in these scenarios is to copy properties or use smart
classes to ship over the wire that hold all of their data in a format that's
easy to reattach in some way. FOr example, you can pass datasets back and
forth and simply pick up the data sets and attach them to your client
object.


+++ Rick ---

--

Rick Strahl
West Wind Technologies
http://www.west-wind.com/
http://www.west-wind.com/weblog/

 

[Chris Dunaway]

On Sat, 28 Feb 2004 00:35:48 -0000, Malek wrote:

Thanks for the response. Perhaps web services are not the way to go for my
project. We offer a service in which all the equipment needed to carry
out that service is maintained at our central facility. We want to give
clients the ability to submit a 'job' over the internet to use our service.
I am creating a 'Thin Client' app to allow them to do this. The web
service will only be accessed by this 'Thin Client' app and not made
available otherwise. This 'Thin Client' will allow the customer to gather
necessary data at their end and submit to our central facility for
processing. We would then provide them with a report with the results of
the processing.

Web services seemed to be a simple way to allow the client app to
communicate with our servers. Do you think remoting would be a more
appropriate method for this type of project?

Thanks again