This is the api for odoo8?

from openerp import models, fields, api
class hr_timesheet_sheet(models.Model):
    _inherit = ["hr_timesheet_sheet.sheet"]
    project_field = fields.Many2one('project.project', 'name') 

and this the old one?:

from openerp.osv import osv, fields, api
class hr_timesheet_sheet(osv.osv):
    _inherit = ["hr_timesheet_sheet.sheet"]
	_columns = {
	'project_field': fields.many2one('project.project', 'name')
	}

What should I use for odoo8 and why?