APEX

Hi all!
In Apex 3.2, I've got an Interactive report with a DML form on a table. My table has a primary key which use a sequence (trigger based). When I created my forms, I specified that I wanted to use an existing trigger as the source type of the primary key.

When I try to create a record, it work. If I try to create a new record and save, my trigger give me an error message because the automatic row processing is trying to update the primary key too. (My trigger on the update specify that the primary key should not be updated).

So my question is : How can I make the automatic row processing update everything but the primary key ? (I noticed that I could have asked APEX to use my SEQUENCE directly instead of the trigger (in the creation Wizard). But I dont know how to change this now that my form is created.)

Is there a source type that I can change in my primary key item ?


Note : My primary key item (id_emp) is protected and hidden. If I display it as "Display only", the update works... But I dont need to see id_emp on my form.