Django form on the model

I have Guest model in my app:

class Guest(models.Model):
event = models.ForeignKey(Event, related_name='guests')
contact = models.ForeignKey(Contact, related_name='guests')
attending_status = models.CharField(max_length=32, choices=ATTENDING_CHOICES, default='no_rsvp')
number_of_guests = models.SmallIntegerField(default=0)
comment = models.CharField(max_length=255, blank=True, default='')
updated = models.DateTimeField(blank=True, null=True)

Event and Contact I fill up by myself in Admin when creating a guest. On the site all I want is a guest to fill up the form where he refreshes his attending status, points out number of guests and leaves a comment.

class RSVPForm(forms.Form):
attending = forms.ChoiceField(choices=VISIBLE_ATTENDING_CHOICES, initial='yes', widget=forms.Radi开发者_JAVA技巧oSelect)
number_of_guests = forms.IntegerField(initial=0)
comment = forms.CharField(max_length=255, required=False, widget=forms.Textarea)

How can I save the changes to the Guest model instance? How can I access the guest's id when saving the changes to his profile?

You are probably looking for Django's ModelForms. Instead of subclassing forms.Form in your RSVPForm class, you should subclass forms.ModelForm. Then you can use the features of the model form class to help you achieve what you want (hide some fields, etc). An example is below:

class RSVPForm(forms.ModelForm):
    class Meta:
        model = Guest
        fields = ('attending_status', 'number_of_guests', 'comment')

This will do essentially what you want, but you will need to remember to provide an instance keyword argument to the form constructor in your view function. This argument is the instance of the Guest model you will be updating with the form.

form = RSVPForm(instance=guest_object)

Now calls to the form.save() method will automatically save the new data to this Guest object instance. You just need to make sure that you always pass the instance keyword argument, even when using request.POST:

form = RSVPForm(request.POST, instance=guest_object)