Django form - keep some POST data -

i writing small django internet store , have encountered problem. namely, print list of products (i need pruduct id) , form buy them on same page.

def order(request):     if request.method == 'post':         form = orderform(request.post)         if form.is_valid():             # post data processing             return httpresponseredirect('/cart/')     else:         form = orderform()      # here use product_id post generate products      # have such id     return render(request, 'order.html', {         'form': form, 'products': products,     }) 

but when wrongly submit form, orderform() called , lose id. hints how solve problem (maybe keep somewhere id)?

edit: store used rent products on given time , adding product cart means create new object rent store information when product has been reserved user

model:

class rent(models.model):      product = models.foreignkey(product)      paid = models.booleanfield()     begin_date = models.datefield(auto_now=false)     end_date = models.datefield(auto_now=false)      begin_hour = models.integerfield(max_length=2, default=00)     end_hour = models.integerfield(max_length=2, default=24) 

and orderform

class orderform(forms.form):     begin_date = forms.datefield(label='date', required=true,                                    widget=extras.widgets.selectdatewidget(years=range(2013, 2015)))     end_date = forms.datefield(required=true, initial=datetime.date.today,                                 widget=extras.widgets.selectdatewidget(years=range(2013, 2015)))     begin_hour = forms.choicefield(required=true, choices=((str(x), x) x in range(0, 25)))     end_hour = forms.choicefield(required=true, choices=(((str(x)), x) x in range(0, 25)))