Django-从预先创建的列表中选择项目和数量

Question

I cannot figure out a suitable solution for what I believe is a beginner problem. Any help is highly appreciated.

The website I am building will be used to plan parties. Two types of people will use it, party organizers and party visitors. The party organizers are able to create a party and select items to be offered to visitors. Items are food and drinks, 1 item = one pizza or one beer.

Users will then be able to confirm participation for the party and select which food and drinks they would like to order and how many. I already created authentication and creation of a party.

Now, my issues are this:

1. How can the organizer create a list of items to be offered to the visitor?
2. How can the visitor select both type of item and quantity?

I have tried with the following code (trimmed down):

models.py:

class ItemType(models.Model):
    """Create items (food and drinks)."""
    name = models.CharField()

class Party(models.Model):
    """Create a party."""
    organizer = models.ForeignKey(User)
    party_name = models.CharField()
    items_to_be_offered = models.ManyToManyField(ItemType)

class PartyRegistration(models.Model):
    """Register for a party / create party registration."""
    party = models.ForeignKey(Party)
    visitor = models.CharField()
    selected_items = models.ManyToManyField()

class ItemSelection(models.Model):
    """Specify which items and number of items the visitor selected."""
    party_registration = models.OneToOneField(PartyRegistration)
    item_type = models.ManyToManyField(ItemType)
    item_quantity = models.PositiveIntegerField()

forms.py

class VisitorRegisterForm(forms.ModelForm):
    """Form to register a visitor."""

    class Meta:
        model = PartyRegistration
        fields = ['visitor', 'selected_items']

views.py

def VisitorRegister(request, pk):
    """Register Visitor to a specific party."""    
    party = get_object_or_404(Party, pk=pk)    

    if request.method == 'POST':
        form = VisitorRegisterForm(request.POST)
        if form.is_valid():
            name_clean = form.cleaned_data['visitor']
            registration = PartyRegistration(party=party, visitor=name_clean)
            registration.save()
            return HttpResponseRedirect(reverse('index'))
    else:
        form = VisitorRegisterForm()

    context = {'form': form, 'party': party}

    return render(request, 'visitor-register.html', context)

Website is Django 2.0, PostgreSQL.

Answer 1

You need a ManyToMany relationship with a through model in this case (order matters, or change the order and quote PartyRegistration ):

class PartyRegistration(models.Model):
    """Register for a party / create party registration."""
    party = models.ForeignKey(Party)
    visitor = models.CharField()
    selected_items = models.ManyToManyField(ItemType, through='ItemSelection')

class ItemSelection(models.Model):
    """Specify which items and number of items the visitor selected."""
    party_registration = models.ForeignKey(PartyRegistration)
    item_type = models.ForeignKey(ItemType)
    item_quantity = models.PositiveIntegerField(default=1)

    class Meta:
        unique_together = ('party_registration', 'item_type')

See https://docs.djangoproject.com/en/2.1/topics/db/models/#intermediary-manytomany