Django - ManyToMany

Question

I'm making a game link site, where users can post links to their favorite web game. When people post games they are supposed to check what category the game falls into. I decided to allow many categories for each game since some games can fall into many categories. So the question is, how do I handle this in my view? And how can I show it as Checkboxes, where at least one has to be checked? And how can I show this as checkboxes in the Admin as well?

Here is the code

Models:

class Category(models.Model): 
        category = models.CharField(max_length=200) 
        def __unicode__(self): 
                return self.category 
class Game(models.Model): 
    name = models.CharField(max_length=200) 
    url = models.CharField(max_length=200) 
    poster = models.ForeignKey(User, related_name='game_poster_set') 
    postdate = models.DateTimeField(default=datetime.now) 
    cats = models.ManyToManyField(Category) 
    hits = models.IntegerField(default=0) 
    post = models.BooleanField(default=False)

---

Views:

def submit(request): 
        form = GameForm(request.POST or None) 
        if form.is_valid(): 
                game = form.save(commit=False) 
                game.poster = request.user 
                game.save() 
                next = reverse('gamesite.games.views.favorites') 
                return HttpResponseRedirect(next) 
        return render_to_response( 
        'games/submit.html', 
        {'form': form}, 
        context_instance = RequestContext(request),)

---

Forms:

class GameForm(forms.ModelForm): 
        name = forms.CharField(max_length=15, label='Name') 
        url = forms.URLField(label='URL', initial='http://') 
        class Meta: 
                model = Game 
                fields = ('name','url')

Thanks!

Answer 1

Although it's not specifically python related, this tutorial makes a great point about M:N relationships. Usually it's advantageous to create a third mapping object that serves as a 1:M between the two objects. This is the way M:N is handled in SQL, and it may make sense in your object model as it will allow you to store additional meta-data...perhaps the percentage that the user thinks the game fits into the genre?

Answer 2

class GameForm(forms.ModelForm): 
        name = forms.CharField(max_length=15, label='Name') 
        url = forms.URLField(label='URL', initial='http://') 
        cats = forms.ModelMultipleChoiceField(widget=forms.CheckboxSelectMultiple(),required=True)
        class Meta: 
                model = Game 
                fields = ('name','url','cats')

that should fix your view, but i'm not sure about the admin. still looking... will edit if i find anything.

Answer 3

Here is how I solved it (Edit: and the admin thing)

Forms:

cats = forms.ModelMultipleChoiceField(widget=forms.CheckboxSelectMultiple, queryset=Category.objects.all())

(It was the queryset part I couldn't find..)

View:

cats = form.cleaned_data['cats']
 game.cats = cats

And that's all the code needed to save the data.

Edit: here is a solution for the admin

Models:

from django.contrib import admin
from django.forms import CheckboxSelectMultiple

class MyModelAdmin(admin.ModelAdmin):
    formfield_overrides = {
        models.ManyToManyField: {'widget': CheckboxSelectMultiple},
    }

Admin:

from gamesite.games.models import Game, MyModelAdmin

admin.site.register(Game, MyModelAdmin)

It's kind of quirky in looks, but works! If someone finds a way to make it more "clean" please post!

Cheers!