Converting a record with its related ones to another and its

Hi All,

I have a situation that in a button click or in a trigger I have to convert a record and its related ones to another record and its relations.

For example I have Order, OrderLine, Invoice and InvoiceItem objects.

For an order that has 3 orderLines I should be able to create an Invoice and InvoiceItems in a way that Order detail will be used to create Invoice record and 3 OrderLine details will be used to create 3 InvoiceItem records with the relationship to the newly created Invoice record.

Something like 

In Rollbase what is the efficient way to achieve this with the help of conversion maps created for Order-->Invoice and OrderLine-->InvoiceItem?

Thank You 
-Ithrees