How to return an ID if I add Data on AddObject?

Question

I'm using the WCF Data Service client and try to add an object to my datacontext (EntityFramework). The Object is added but I can't use the id afterwards. Is there any possibility that after triggering the SaveChanges method, the object directly gets the auto generated id?

Order order=new Order();
order.name="test";
context.AddObject("Order", order);
if (await context.SaveChanges()) //Extension method on my context to save changes async
{
  System.Diagnostics.Debug.WriteLine(order.id); //output: 0
}

My extension method looks like this:

public partial class MyEntities
{
  public async Task<bool> SaveChanges()
  {
    var queryTask = Task.Factory.FromAsync(this.BeginSaveChanges(null,null), asResult =>
    {
        return(asResult.IsCompleted);
    });
    return await queryTask;
  }
}

I tried also to extend the AddObject method, but this approch also returns a 0 value:

    internal async void AddObject<TResult>(object entity) where TResult : IExtend
    {
        base.AddObject(entity.ToString().Split('.').Last(), entity);
        if (await this.SaveChanges())
        {
            System.Diagnostics.Debug.WriteLine(((TResult)entity).id); //output: 0
        }
    }

Answer 1

I missed the EndSaveChanges function. When I change my extended function to this, the object id is updated.

    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;
    }