Creating records using related data and obtaining their primary keys?

I've got a Db structure where I have tblStock and tblStockLines related by fk_stockID in the lines table.

When adding a new line to an existing stock or a whole new set (stock and stock line) - how can I get the primary key of the newly inserted records? Specifically the child object's primary key.

Almost like using the fields command when using POST or PUT that results in a lookup of the inserted data.