Pre-populate an inline FormSet?

Fred_Larson_10077 0
Viewed 22317

I'm working on an attendance entry form for a band. My idea is to have a section of the form to enter event information for a performance or rehearsal. Here's the model for the event table:

class Event(models.Model):
    event_id = models.AutoField(primary_key=True)
    date = models.DateField()
    event_type = models.ForeignKey(EventType)
    description = models.TextField()

Then I'd like to have an inline FormSet that links the band members to the event and records whether they were present, absent, or excused:

class Attendance(models.Model):
    attendance_id = models.AutoField(primary_key=True)
    event_id = models.ForeignKey(Event)
    member_id = models.ForeignKey(Member)
    attendance_type = models.ForeignKey(AttendanceType)
    comment = models.TextField(blank=True)

Now, what I'd like to do is to pre-populate this inline FormSet with entries for all the current members and default them to being present (around 60 members). Unfortunately, Django doesn't allow initial values in this case.

Any suggestions?

django-forms django python
10 Answers

So, you're not going to like the answer, partly because I'm not yet done writing the code and partly because it's a lot of work.

What you need to do, as I discovered when I ran into this myself, is:

  1. Spend a lot of time reading through the formset and model-formset code to get a feel for how it all works (not helped by the fact that some of the functionality lives on the formset classes, and some of it lives in factory functions which spit them out). You will need this knowledge in the later steps.
  2. Write your own formset class which subclasses from BaseInlineFormSet and accepts initial. The really tricky bit here is that you must override __init__(), and you must make sure that it calls up to BaseFormSet.__init__() rather than using the direct parent or grandparent __init__() (since those are BaseInlineFormSet and BaseModelFormSet, respectively, and neither of them can handle initial data).
  3. Write your own subclass of the appropriate admin inline class (in my case it was TabularInline) and override its get_formset method to return the result of inlineformset_factory() using your custom formset class.
  4. On the actual ModelAdmin subclass for the model with the inline, override add_view and change_view, and replicate most of the code, but with one big change: build the initial data your formset will need, and pass it to your custom formset (which will be returned by your ModelAdmin's get_formsets() method).

I've had a few productive chats with Brian and Joseph about improving this for future Django releases; at the moment, the way the model formsets work just make this more trouble than it's usually worth, but with a bit of API cleanup I think it could be made extremely easy.

James_Bennett_280700

Here is how I solved the problem. There's a bit of a trade-off in creating and deleting the records, but the code is clean...

def manage_event(request, event_id):
    """
    Add a boolean field 'record_saved' (default to False) to the Event model
    Edit an existing Event record or, if the record does not exist:
    - create and save a new Event record
    - create and save Attendance records for each Member
    Clean up any unsaved records each time you're using this view
    """
    # delete any "unsaved" Event records (cascading into Attendance records)
    Event.objects.filter(record_saved=False).delete()
    try:
        my_event = Event.objects.get(pk=int(event_id))
    except Event.DoesNotExist:
        # create a new Event record
        my_event = Event.objects.create()
        # create an Attendance object for each Member with the currect Event id
        for m in Members.objects.get.all():
            Attendance.objects.create(event_id=my_event.id, member_id=m.id)
    AttendanceFormSet = inlineformset_factory(Event, Attendance, 
                                        can_delete=False, 
                                        extra=0, 
                                        form=AttendanceForm)
    if request.method == "POST":
        form = EventForm(request.POST, request.FILES, instance=my_event)
        formset = AttendanceFormSet(request.POST, request.FILES, 
                                        instance=my_event)
        if formset.is_valid() and form.is_valid():
            # set record_saved to True before saving
            e = form.save(commit=False)
            e.record_saved=True
            e.save()
            formset.save()
            return HttpResponseRedirect('/')
    else:
        form = EventForm(instance=my_event)
        formset = OptieFormSet(instance=my_event)
    return render_to_response("edit_event.html", {
                            "form":form, 
                            "formset": formset,
                            }, 
                            context_instance=RequestContext(request))
user_2891400
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