Re: modelformset question - interspersing extra forms among existing forms

Hi,

Your case is complicated enough that I'd actually recommend not using formsets here and processing a list of plain ModelForms yourself in the view. I bet formsets will ending out getting in your way.

Here's a some messy code:

class EntryForm(forms.ModelForm):
    race_number = Entry._meta.get_field('race_number').formfield(required=False)
    class Meta:
        model = Entry
        fields = ['race_number']

def the_view(request, athlete_id):
    athlete = get_object_or_404(Athlete, id=athlete_id)
    existing = {e.category_id: e for e in athlete.entry_set.all()}
    entries = []
    for category in Category.objects.order_by('particular'):
        entries.append(existing.get(category.pk, Entry(athlete=athlete, category=category)))
    if request.method = 'POST':
        forms = [EntryForm(request.POST, instance=e, prefix=e.category.pk) for e in entries]
        if all([f.is_valid() for f in forms]):  # be sure to call is_valid() on every form
            for entry in entries:
                if entry.race_number:
                    entry.save()
                if entry.pk and not entry.race_number:
                    entry.delete()
    else:
        forms = [EntryForm(instance=e, prefix=e.category.pk) for e in entries]
    return render(request, 'template.html', {'athlete': athlete, 'forms': forms})

{% for form in forms %}
Category: {{ form.instance.category }}
{{ form }}
{% endfor %}

Collin

On Monday, December 29, 2014 6:07:19 PM UTC-5, Richard Brockie wrote:

Hi,

I have the following pseudo model that I will use as the basis of a modelformset:

class Entry:
    athlete = ForeignKey(athlete)
    category = ForeignKey(category)
    race_number = IntegerField

I have a page that displays each athlete's details so the choice of athlete has already been made. I want to add a formset that allows a user to specify a race_number for each of the possible categories available.

An obvious way would be for there to be one Entry for each athlete/category, but in practise this will result in a large entry table that is only ~10% actual data, with the rest being superfluous rows. I'd prefer to avoid this.

Let's assume that an athlete is already entered in 2 categories out of a possible 10. The queryset will return the 2 existing entries, and I can use extra=8 to add in the other possibilities. However, I am not yet done. I want to do the following and would like advice on how to accomplish this:

1. The category for each the 8 possible new entries needs to be assigned before displaying the form - I already know what they are and want to display these categories to the user, leaving the race_number as the only input field.
   
2. The categories have a particular (chronological) order that I want respected in displaying the forms to the user, so the 2 existing and 8 possible new categories need to be interspersed to follow the correct order.
3. When it comes time to save the formset, I want only those categories that have been changed by having a race_number assigned or removed to be saved. I want the entries where the race_number has been removed to remain in the entry table. I think I need a way to detect and remove the forms that have not been changed by the user before saving the formset.

Any pointers as to how to do this?

Thanks!
R.

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