I need to pass a custom field value from my reservation form view, to invoice lines in invoice form view. Like odoo passes the products details from sale order to invoice lines. What method does odoo use? ( invoice "open" automatically when the state for my reservation is finished)

This my value
partner_id (cars_reservation)>>> partner_id (account.invoice)
product_id (cars_reservation)>>> product_id (account.invoice.line)
product_price (cars_reservation)>>> price_unit (account.invoice.line)
price_total (cars_reservation)>>> amount_total (account.invoice)
this my Code class

class cars_reservation(models.Model): _name = 'cars.reservation' _rec_name = 'name_reservation'

 def action_draft(self, cr, uid, ids, context=None): return self.write(cr,uid,ids,{'state' : 'draft'})

def action_done(self, cr, uid, ids, context=None): return self.write(cr,uid,ids,{'state' : 'finished'})

def action_cancel(self, cr, uid, ids, context=None): return self.write(cr,uid,ids,{'state' : 'canceled'})

name_reservation = fields.Char('number', size=64, readonly=True)
reservation_date_time = fields.Datetime('Date')
partner_id = fields.Many2one('res.partner', string='Partner', required=True)
product_id = fields.Many2one('product.product', string='Product')
product_price = fields.Integer('price')
price_total = fields.Integer('price')state = fields.Selection([ ('new', 'new'), ('finished', 'finished'), ('canceled', 'canceled') ], 'state', readonly=True, select=True)

_defaults = { 'state': lambda * a:'new', 'name_reservation': lambda self,cr,uid,context={}: self.pool.get('ir.sequence').get(cr, uid, 'reg_code'), }