wcf data services saving relational data in single click - wcf

Question

I'm using WCF data services in Windows phone 7, I want to save relational data in single click how could I do that?
it's think 2 table : Category and Products
I want to save data UI :
From Cateogry Table :-
CategoryId : (auto increment)
CategoryName : abc
From product Table :-
ProductId :-(auto increment)
CategoryId :- ? ( not sure how could I retrieve )
ProductsName : xyz
on button save click:
I want to insert above data in appropriated table , how could I do that?
I am using following code for add one table data :
try
{
context = new NorthwindEntities(NorthwindUri);
context.AddToProducts(product);
context.BeginSaveChanges(new AsyncCallback((result) =>
{
bool errorOccured = false;
// Use the Dispatcher to ensure that the
// asynchronous call returns in the correct thread.
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
context = result.AsyncState as NorthwindEntities;
try
{
// Complete the save changes operation and display the response.
DataServiceResponse response = context.EndSaveChanges(result);
foreach (ChangeOperationResponse changeResponse in response)
{
if (changeResponse.Error != null) errorOccured = true;
}
if (!errorOccured)
{
MessageBox.Show("The changes have been saved to the data service.");
}
else
{
MessageBox.Show("An error occured. One or more changes could not be saved.");
}
}
catch (Exception ex)
{
// Display the error from the response.
MessageBox.Show(string.Format("The following error occured: {0}", ex.Message));
}
});
}), context);
}
catch (Exception ex)
{
MessageBox.Show(string.Format("The changes could not be saved to the data service.\n"
+ "The following error occurred: {0}", ex.Message));
}

Answer 1

In OData relationships are not represented as foreign keys, instead they are represented as navigation properties. And then you manipulate them through manipulating links in the client library.
Take a look at this article: http://msdn.microsoft.com/en-us/library/dd756361(v=vs.103).aspx
You can call multiple methods which modify data and then call SaveChanges to send them all to the server.
Note though, that if the server requires referential integrity and you're for example adding two related entities at the same time, you might need to use SaveChanges(Batch) (which makes the client send everything in one request and thus allows the server to process it as a single transaction).