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Need help on passing custom objects (classes) to web service

Re: Need help on passing custom objects (classes) to web service

Manohar Kamath
3/5/2005 10:35:16 AM

dotnet web services:

The methods are never serialized in web services, only data (state) is. You
could serialize and de-serialize into the same type, but it will require
some manual changes to your proxy classes (you need to reference the
employee assembly, instead of proxy-generated types).

--
Manohar Kamath
Editor, .netWire
www.dotnetwire.com

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Need help on passing custom objects (classes) to web service

Noel
3/5/2005 9:45:45 PM

Hello,

I'm currently developing a web service that retrieves data from an employee
table. I would like to send and retrieve a custom employee class to/from the
webservice. I have currently coded the custom employee class and have built
it as a separate library (employee.dll). This employee.dll is being
referenced by both the web service and the windows application.

I face the following problem when I send this class to the webservice.

1. The procedures and functions are not getting serialized. i.e. when the
webservice returns this class, I'm unable to access the procedures and
functions for manipulating the data in the class.

Could someone let me know how I could solve this issue? I'm in trouble and
am badly in need of help. Please advise.

Thanks,
Noel

Re: Need help on passing custom objects (classes) to web service

Manohar Kamath
3/7/2005 8:57:04 AM

Could you please post the code snippets? Thanks!

--
Manohar Kamath
Editor, .netWire
www.dotnetwire.com

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Re: Need help on passing custom objects (classes) to web service

Noel
3/7/2005 10:44:12 AM

Thanks for the reply Manohar.

When I try to reference the employee assembly instead of proxy-generated
types, I get an invalid type-cast error. BTW, I'm trying to pass the
employee object to the web-service as a reference. Is there a way to get
around the invalid type cast error?

Thanks in advance.

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Re: Need help on passing custom objects (classes) to web service

Manohar Kamath
3/7/2005 12:54:04 PM

Noel,

Here's the problem:

You are sending in obj, which is of different type than the proxy type:

wsEmp.GetData(obj)

It is expecting: EmployeeWebService.EmployeeObject -- this is a proxy type,
whereas your EmployeeObject is in a different namespace.

To remedy this, you need to manually change your proxy class, remove the
type EmployeeWebService.EmployeeObject from the class, and add a reference
to your Employee library in the proxy class (using Imports). This tricks the
compiler into thinking that you are using the proxy type, while it is
actually using your custom type.

Hope that helps.

--
Manohar Kamath
Editor, .netWire
www.dotnetwire.com

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Re: Need help on passing custom objects (classes) to web service

Manohar Kamath
3/7/2005 12:55:35 PM

Yes, you will lose the changes to the proxy classes if you re-generated the
proxy class. However, this is one of those "to-do" if this ever happened.
And also, once you have the web service solidified, the proxy class should
never change -- as a change would mean a change in the version.

--
Manohar Kamath
Editor, .netWire
www.dotnetwire.com

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Re: Need help on passing custom objects (classes) to web service

Glenn
3/7/2005 5:19:51 PM

Noel

What about creating serialisable types from schema definitions and then
passing the xml as a XmlNode or XmlDocument and then deserialising and
reserialising inside the web service. That way if anyone else needs to use
your web service, you only need publish the schema and wsdl and anyone could
bind to it.

As for the employee.dll, could you expose the functionality as a web
service? It may make your application a bit chatty on the wire depending on
how you use it, but a least you won't have as many deployment headaches
(albeit reduced with .net).

Apologies if I've misunderstood Manohar's comment, but manual changes to the
web service proxy would be lost if you made a change to the web service and
refreshed the reference at the client end.

HTH

Glenn

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Re: Need help on passing custom objects (classes) to web service

Glenn
3/7/2005 5:42:20 PM

Noel

Not a problem, but can't do it this evening, Man City vs Bolton and I've got
a date with the pub, I'll post some more detail tommorrow morning (GMT ).

Cheers

Glenn

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Re: Need help on passing custom objects (classes) to web service

Noel
3/7/2005 11:00:44 PM

There is so little code, that I thought I'd explain a bit more. Please do
not mistake me, just let me know if you still need the code and I'll send it
across.

This is what I have in the project:

1. Employee project (stand alone executable - windows application)
2. Employee Class Built as a library. This has been compiled as a library
just to allow me to use in both the web services as well as the Employee
Project.
3. Web service that interfaces with the database.

The web service and the employee project reference the employee library.

In the windows application, I create an instance of webservice and pass the
employee object as reference, like:

Dim wsEmp as New EmployeeWebService
Dim obj As EmployeeObject
' obj is sent across by reference - Error occurs here
' (like Employee Object cannot be
' typecast to ' EmployeeWebService.EmployeeObject)
wsEmp.GetData(obj)

In the web service, I create an instance of the employee object and fill it
with data from the webservice, like:

Sub GetData(ByRef obj As EmployeeObject)
obj = New EmployeeObject
' Access database and fill Employee object with data
FillData(obj)
End Sub

I get an error "Invalid Typecast" in wsEmp.GetData(obj).

Both the objects (Windows and Web Service) are the same and refer to
Common.EmployeeObject. I'm wondering if I need to mark the
Common.EmployeeObject as serializable (Not sure though).

Thanks in advance.

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Re: Need help on passing custom objects (classes) to web service

Noel
3/7/2005 11:03:43 PM

Glenn, I like your idea. Could you please point me to some source code or
website where I could learn how to do this? I'll be glad if you could help.

Thanks in advance.

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RE: Need help on passing custom objects (classes) to web service

Raj Tripathi
3/8/2005 4:43:01 AM

If you want to return binary objects from the webservice the only way is to
mark your object as [Serializable] then:

On Server:
[WebMethod]
[SoapDocumentMethod(ParameterStyle=SoapParameterStyle.Bare)]
byte[] GetEmployee()
{
Employee employee = new Employee("Eric Cartmen");
MemoryStream memoryStream = new MemoryStream();
BinaryFormatter formater = new BinaryFormatter();
formater.Serialize(memoryStream, employee);
return memoryStream.ToByteArray();
}

On Client:
Employee GetEmployee()
{
byte[] rawEmployee = Service.GetEmployee();
BinaryFormatter formater = new BinaryFormatter();
return (Employee) formater.Deserialize(rawemployee);

----------------------------------------------------------------------------------------------
Lookup MSDN for [SoapDocumentMethod(ParameterStyle=SoapParameterStyle.Bare)]

!!! BEWARE Binary formating is not version safe. i.e. If you change the
version of
your Employee class make shure that Server and Client use the same version.

If this is not accepteble to you use XML Serialization.

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Re: Need help on passing custom objects (classes) to web service

Noel
3/8/2005 10:39:48 AM

Could you please throw some light on how the versioning needs to be done for
the proxy class?

One more question regarding the custom class:

I'm not sure what's the preferred/best method to retrieve the records from
the webservice. Which one is better when deciding to retrieve data from web
service?

1. Using Datasets (Multiple datatables can be returned. But could this make
the web service slower than when using custom objects)
2. Custom objects

BTW, when deciding to use custom objects. How should the records be stored
inside the object (I mean what's the industry standard or preferred method
of storing multiple records in a custom object?) Should a dataset/datatable
be used inside the custom object to store data or is there another better
method?

Another question/topic:

The architecture that I want to follow is GUI -> Web service -> Business
Objects -> database.

I would like the application to be highly scalable and load balanced.
Therefore I would like to scale it at the business objects level. If I have
multiple servers with the Business Objects installed/running. How could I
let the web service know

1. Which server to use (depending on load balancing.) BTW to load balance
should I incorporate any logic to the application/webservice?
2. How to supply/notify my web service at run-time the servers that have the
Business Objects running?

Thanks in advance for your valuable inputs.

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Re: Need help on passing custom objects (classes) to web service

Glenn
3/8/2005 10:50:15 AM

Noel

The XML part or exposing the employee.dll functionality as a web service?

With regards to XML serialization

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnexxml/htm
l/xml01202003.asp

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/
frlrfsystemxmlserialization.asp

If your using VS.NET you could use the rather good XML Designer to build
your schema definitions.

As for exposing functionality on the web for an existing DLL, a personal
preference is to create a thin web service wrapper type around the existing
class. Any overloaded methods can be handled using the MessageName property
of the WebMethod attribute.

I've have to say that most of the work I've been doing with XML and web
services in general has been processing data in a single hit. Dealing with
rich client applications may not lend itself to using a serialisation
mechanism.

Thinking about it a bit more, DataSets may be a better solution than having
to worry so much about the serialisation mechanism. I've not personally
used them in web services having been told by a supposedly more learned
colleague not to, but it may be perfect for what you want to do.

I'd check out these articles before attempting to use DataSets with web
services

http://www.oreillynet.com/pub/wlg/2142

http://weblogs.asp.net/aaguiar/archive/2004/06/03/147208.aspx

Sorry if I've not been much help, I'm extremely hungover.

Glenn

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