Hello guys, my problem is that I'd like add a department field in res.partners for group by deparment in calendar module, I added the following lines (dept_prueba is the field that I added):

class res_partner(osv.Model):

    _inherit = 'res.partner'

    _columns = {

        'calendar_last_notif_ack': fields.datetime('Last notification marked as read from base Calendar'),

        'dept_prueba': fields.many2one('hr.department'),

    }

But in Odoo I got this error 

ProgrammingError: column res_partner.dept_prueba does not exist
LINE 1: ...mployee","res_partner"."birthdate" as "birthdate","res_partn...

Could someone help me? Thanks!