How to set a predefined form value from a link in Django?

Question

My project is laid out like so:

1. page
   has many: categories

2. category
   belongs to: page
   has many: items

3. item
   belongs to: category

Answer 1

So, the way to do this is to exclude it from the form completely and set it in the view on save.

class ItemForm(forms.ModelForm):
    class Meta:
        model = Item
        exclude = ('category',)

and the view:

def create_item(request, category_id):
    if request.method == 'POST':
        form = ItemForm(request.POST)
        if form.is_valid():
            item = form.save(commit=False)
            item.category_id = category_id
            item.save()
            return redirect(...)
    ...etc...

which is served via a url:

url(r'^create_item/(?P\d+)/$, 'create_item', name='create_item'),

and which you can therefore link to from your categories list:

{% for category in categories %}
    
{{ category.name }} - Create item
{% endfor %}