Hi Vipin Appu,
I'm not that sure if your model really fits. Can an instance of a TRANSCATION (btw. is it TRANSCATION or TRANSACTION) exist without a CUSTOMER? If no, TRANSCATION should be a subnode of your CUSTOMER.
If your TRANSCATION is a subnode of your CUSTOMER you can get all TRANSCATIONS for a CUSTOMER by following the association (retrieve_by_association()) to the TRANSCATION. If it's really two BOs, you should modle a Cross BO association. But in anycase, imho it's not neccessary to implement this.
It's also not a good idea to call the queries, you should always use the retrieve-methods provided by the service manager or the io_read instance.
Cheers,
Martin