Hi Nguyen,

This is because your model cinema.seat has no field name.
By default Odoo will build the name that is shown in a many2one with the field 'name'.
If you don't have a field named 'name' you'll need to define your own with the _rec_name parameter though.
Just add it to your cinema.seat model like this:

class CinemaSeat(models.Model):
    _name = 'cinema.seat'
    _rec_name = 'seat_number'

If you want to go further and build a whole custom title you can do it too. You just need to add a function "name_get" to build your own name then. For example:

@api.multi
def name_get(self):
    result = []
    for record in self:
        record_name = record.movie + ' - ' + record.seat_number
        result.append((record.id, record_name))
    return result

Regards,
Yenthe