Zahin,

The domain section is evaluated at ORM and it will not parse any postgresql keywords. What it does it evaluating the OpenERP fields on the left.

I see that you might have misunderstood domain meaning. [('extract(month from cover_date)', '=', month)] is the wrong expression.

The real meaning of the clause(domain) is the first element is field of openerp model, second one is operator and the third one is value you want to operate on.

Hope this helps. Thanks.