Choose primary key for CMR entity beans

[John King]

Hi everyone,
I have a question on choose primary key for CMR entity beans. I'm using following entity beans:
Customer, Order, and LineIterm. They have their own primary key: customerId for Customer, orderId for Order,
and lineItermId for LineIterm. Customer has a orderId as its foreign key while Order has customerId
and lineItermId as its foreign keies. One Customer may have many Orders, and one Order may have many
LineIterms. I'm using CMR, so they are jared together. When I specified
<primkey-field> with different cmp field (customerId for Customer, orderId for Order, lineItermId for
LineIterm) in ejb-jar.xml. I got following error when I try to put data in DB:
"When a cmp-field and cmr-field are mapped to the same column, the
setXXX method for the cmp-filed may not be called."
If I use customerId for all entity beans' <primkey-field>, it works fine.
I do not understand.
I read some examples on CMR entity beans, and find all of them are using same
<primkey-field>. My question
is whether I can use different primary key for different CMR entity bean and why?
Thanks for any inputs.