View and primary key

I have set up a view with rules for insert,update and delete. I would like to
be able to use this view from OpenOffice, however it will not allow editing
of a table without a primary key. I cannot create a primary key because
Postgresql says the column does not have a NOT NULL constraint. This column
in the underlying table is NOT NULL. Is there a way to create a primary key
on a view?

Thank you
Adrian Klaver