multiple object

How to find a multiple object (composition) by parent Id

Dear all,
Sorry in advance, this is probably a very stupid question but I am really stuck on this since the last week...

My BDM contains 2 business objects: "CustomerOrder" & "orderItem".
"CustomerOrder" includes a multiple attribute type "orderItem" (composition) which is the child object to input the items ordered.

I can't succeed to write the customer query in the BDM definition that would find the list of items based on the parent id (the customer order id).. In the studio h2 database, the column name is "CUSTOMERORDER_PID" for this parent Id.