Re: Formset questions: data vs. initial values

Anyone please?

Best regards,
Carsten


Am 07.09.2015 um 21:18 schrieb Carsten Fuchs:
> Dear Django group,
>
> after having read all of the Django docs that I could find, I still have two questions
> about the proper use of formsets. Summary first:
>
> 1. What is a good way to make sure the data received in the POST request agrees with
> the "initial" data (number of items and items order is as expected)?
>
> 2. What is a good way to augment each form with additional data that is only used for
> decoration (rendering additional information) in the template, but is not a form field?
>
>
> More details:
>
> In a single view, I would like to let the user edit calendar entries, i.e. one CharField
> value for each day in a month. The related model is:
>
>
> from django.db import models
>
> class CalendarEntry(models.Model):
> ref_date = models.DateField()
> entry = models.CharField(max_length=40, blank=True)
>
>
> An important issue is that we don't create an instance of CalendarEntry for each day in
> a month, but only for those that actually have an entry! However, the formset that is
> presented to the user should of course have one "entry" field for each day in the month
> (properly initialized if we have a related CalenderEntry instance, blank otherwise).
>
> Thus, it seems that a ModelForm for CalendarEntry cannot be used, because we need some
> forms for which a CalendarEntry instance does not exist, but the form instance must
> still exist and be initialized with a date (and an empty "entry" field).
>
> Therefore, I made a simple form like this, mimicing the model:
>
>
> from django import forms
>
> class ExampleForm(forms.Form):
> ref_date = forms.DateField(widget=forms.HiddenInput())
> entry = forms.CharField(required=False, max_length=40)
>
>
> The date field is hidden, because the user is not supposed to change it. But we need it
> for reference later, when the POST data is processed. (It could possibly be omitted in
> this example, but if this was not the days in a month but the students in a class, it
> would be the only reliable reference connecting the value to the student.)
>
> Now, let's suppose I came up with a list of initial values, both when the formset is
> first created in the GET request, and also later when the data is submitted in the POST
> request. For example like this:
>
>
> # Example is specific to September:
> from datetime import date
> september_inits = [{"ref_date": date(2015, 9, i + 1)} for i in range(30)]
>
> for ce in CalendarEntry.objects.filter(ref_date__year=2015, ref_date__month=9)
> september_inits[ce.ref_date.day-1]["entry"] = ce.entry
>
>
> Now the view is implemented like this:
>
>
> from django.forms.formsets import formset_factory
> from django.shortcuts import render_to_response
> from myapp.forms import ExampleForm
>
> def example_view(request):
> september_inits = [...] # as above
> ExampleFormSet = formset_factory(ExampleForm)
>
> if request.method == 'POST':
> formset = ExampleFormSet(request.POST)
>
> # ~~~~~ Question 1 ~~~~~
> # What is the best way (or: a proper way) to check if formset
> # agrees to september_inits? Can I use
> # formset = ExampleFormSet(request.POST, initial=september_inits)
> # then follow
> https://docs.djangoproject.com/en/1.8/topics/forms/formsets/#custom-formset-validation ?
> # If so, how to access the "initial" data??
>
> if formset.is_valid():
> # ...
> pass
> else:
> formset = ExampleFormSet(initial=september_inits)
>
> # ~~~~~ Question 2 ~~~~~
> # What is the best way (or: a proper way) to add per-form information,
> # e.g. "September 24th is a holiday"?
>
> return render_to_response('manage_articles.html', {'formset': formset})
>
>
> The two questions have been reformulated as comments above.
> Any help would very much be appreciated!
>
> Many thanks and best regards,
> Carsten
>

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