Pre-populate an inline FormSet?

Question

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

Answer 1

Django 1.4 and higher supports providing initial values.

In terms of the original question, the following would work:

class AttendanceFormSet(models.BaseInlineFormSet):
    def __init__(self, *args, **kwargs):
        super(AttendanceFormSet, self).__init__(*args, **kwargs)
        # Check that the data doesn't already exist
        if not kwargs['instance'].member_id_set.filter(# some criteria):
            initial = []
            initial.append({}) # Fill in with some data
            self.initial = initial
            # Make enough extra formsets to hold initial forms
            self.extra += len(initial)

If you find that the forms are being populated but not being save then you may need to customize your model form. An easy way is to pass a tag in the initial data and look for it in the form init:

class AttendanceForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        super(AttendanceForm, self).__init__(*args, **kwargs)
        # If the form was prepopulated from default data (and has the
        # appropriate tag set), then manually set the changed data
        # so later model saving code is activated when calling
        # has_changed().
        initial = kwargs.get('initial')
        if initial:
            self._changed_data = initial.copy()

    class Meta:
        model = Attendance