res_config_settings

1：定义字段 field_name
2：为字段定义 set_field_name  和 get_default_field_name  方法

# set max_sale_discount  at  menu  SET/Generation/Sale
class sale_config_settings(osv.osv_memory):
    _inherit = 'sale.config.settings'
    _columns = {
       'max_sale_discount': fields.float('Set the max sale discount',  digits=(2,2)),
     }
    def get_default_max_sale_discount(self, cr, uid, ids, context=None):
        config_parameter_obj = self.pool.get("ir.config_parameter")
        max_sale_discount = config_parameter_obj.get_param(cr, uid, "max_sale_discount", context=context)
        return {'max_sale_discount' : float(max_sale_discount), }
    
    def set_max_sale_discount(self,cr,uid,ids,context=None):
        config_parameter_obj = self.pool.get("ir.config_parameter")
        for record in self.browse(cr, uid, ids, context=context):
            config_parameter_obj.set_param(cr, uid, "max_sale_discount", str(record.max_sale_discount) )