Hi,
the ordercollection is the Customer's property based on the corresponding relation (you should have such collection property generated right?), and it is actually filled at query time for each customer from the datasource by the use of a prefetch path:
the corresponding code makes the trick:
PrefetchPath2 path = new PrefetchPath2((int)EntityType.CustomerEntity);
path.Add(CustomerEntity.PrefetchPathOrderCollection, 5, null, null,
new SortExpression(OrderFields.OrderDate | SortOperator.Descending));
_customerDS.PrefetchPathToUse = path;
Then you should have a look at the corresponding section in the manual to see how to deal with prefetch paths.
Cheers