Example Gateway services for $expand and deep insert

Dear Experts,

I am trying to practice $expand and deep insert. Is there any blogs that could help me to build a custom Sales Order/Item gateway service, where records could be extracted through $expand and new records can be inserted through deep insert ?

I find standard flight service like below, which gives me the results and i can view them in json format. But, unable to see the design of the service in gateway transaction SEGW.

http://<host>:<port>/sap/opu/odata/IWFND/RMTSAMPLEFLIGHT/FlightCollection?$expand=FlightCarrier

Thanks and Regards.