TO retrieve all children projects of project ids in project module and return a dictionary mapping each project to appiar its parent.id in parent project in project module (or None)in openerp. use this code given below in .py file in openerp.

def _get_project_and_children(self, cr, uid, ids, context=None):

        res = dict.fromkeys(ids, None)
        while ids:
            cr.execute("""
                SELECT project.id, parent.id
                FROM project_project project, project_project parent, account_analytic_account account
                WHERE project.analytic_account_id = account.id
                AND parent.analytic_account_id = account.parent_id
                AND parent.id IN %s
                """, (tuple(ids),))
            dic = dict(cr.fetchall())
            res.update(dic)
            ids = dic.keys()
        return res