How to extend a WCF Data Services context class on clientside? - wcf

Question

I'm using the following code to extend my Service-Context with a FullName on clientside:
public partial class Customer {
public string FullName
{
get
{
return string.Concat(LastName, (FirstName == "" ? "" : ", "), FirstName);
}
}
}
That works fine, until it comes to the point where I need to Add a new Object to the Context with the AddOBject Method. It throws an Exception. When I remove the FullName extension th AddObject method saves the new Object to the database.
What is the best way to extend my Context and still make it Update- and Insertable?
Edit: The DataServiceRequest Exception:
System.Data.Services.Client.DataServiceRequestException was not handled by user code.
HResult=-2146233079
Message=Fehler beim Verarbeiten dieser Anforderung.
Source=Microsoft.Data.Services.Client.WindowsStore
StackTrace:
at System.Data.Services.Client.SaveResult.HandleResponse()
at System.Data.Services.Client.BaseSaveResult.EndRequest()
at System.Data.Services.Client.DataServiceContext.EndSaveChanges(IAsyncResult asyncResult)
at Pointsale.Client.Service.PointsaleEntities.<SaveChanges>b__0(IAsyncResult asResult) in c:\Users\Jan\Desktop\pointsale_worksapce\pointsale.client\Helper\TenantHelper.cs:line 98
at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult iar, Func`2 endFunction, Action`1 endAction, Task`1 promise, Boolean requiresSynchronization)
InnerException: System.Data.Services.Client.DataServiceClientException
HResult=-2146233079
Message=<?xml version="1.0" encoding="utf-8"?><m:error xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata"><m:code /><m:message xml:lang="de-DE">Error occurred while processing this request.</m:message></m:error>
StatusCode=400
InnerException:
And the SaveChanges method overide to get it async:
public async Task<DataServiceResponse> SaveChanges()
{
var queryTask = Task.Factory.FromAsync(this.BeginSaveChanges(null, null), asResult =>
{
var result = this.EndSaveChanges(asResult);
return result;
});
return await queryTask;
}
On EndSaveChanges the error occures.