Using Django Properties with Formsets

The issue you're encountering is a common one when working with Django properties and forms. Django formsets (and forms in general) only work with actual model fields, not with properties. This is why you're getting the "Unknown field(s) (amount)" error.

Here are a few approaches to solve this problem:

Option 1: Create a Custom Form with a Field for amount

Create a custom form that explicitly defines the amount field and handles the conversion between the form field and your model's underlying fields:

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class AdjunctForm(forms.ModelForm):
    amount = forms.CharField()  # Or use a more specific field type if needed

    class Meta:
        model = RecipeAdjunct
        fields = ['adjunct', 'time_to_add', 'intended_use', 'recipe_notes']
        # Note: amount is defined separately, not in fields

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        # If we're editing an existing instance, populate the amount field
        if self.instance and self.instance.pk:
            self.fields['amount'].initial = self.instance.amount

    def save(self, commit=True):
        instance = super().save(commit=False)
        # Set the amount property which will handle the logic to set the right field
        instance.amount = self.cleaned_data['amount']
        if commit:
            instance.save()
        return instance

Option 2: Modify Your View to Handle the Property

When using recipe.adjuncts.all().values() for the initial data, it won't include properties. You need to manually prepare the initial data:

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def editAdjuncts(request, pk=None):
    if request.method == "GET":
        if pk:
            recipe = Recipe.objects.get(pk=pk)
            if len(recipe.adjuncts.all()) > 0:
                adjunct_set_form = formset_factory(AdjunctForm, extra=0, can_delete=True, can_delete_extra=True)
                
                # Manually prepare initial data including the amount property
                initial_data = []
                for adjunct in recipe.adjuncts.all():
                    adjunct_data = {
                        'adjunct': adjunct.adjunct,
                        'amount': adjunct.amount,
                        'time_to_add': adjunct.time_to_add,
                        'intended_use': adjunct.intended_use,
                        'recipe_notes': adjunct.recipe_notes,
                    }
                    initial_data.append(adjunct_data)
                
                adjunct_set = adjunct_set_form(initial=initial_data)
            else:
                adjunct_set = formset_factory(AdjunctForm, extra=1)()
        context = {'recipe': recipe, 'adjunct_set': adjunct_set}
        return render(request, 'batchthis/editAdjuncts.html', context)

Option 3: Create a Custom Field for Your Form

If you need to use a ModelFormset, you could create a custom form field that handles the conversion between your property and the underlying fields:

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class RecipeAdjunctForm(forms.ModelForm):
    amount = forms.CharField()  # Or a more specific field type

    class Meta:
        model = RecipeAdjunct
        fields = ['adjunct', 'time_to_add', 'intended_use', 'recipe_notes']

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        if self.instance.pk:
            self.fields['amount'].initial = self.instance.amount

    def clean(self):
        cleaned_data = super().clean()
        # Any validation for amount can go here
        return cleaned_data

    def save(self, commit=True):
        instance = super().save(commit=False)
        instance.amount = self.cleaned_data.get('amount')
        if commit:
            instance.save()
        return instance

Then in your view:

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adjunct_set_form = modelformset_factory(RecipeAdjunct, form=RecipeAdjunctForm, extra=0, can_delete=True)
adjunct_set = adjunct_set_form(queryset=recipe.adjuncts.all())

Choose the approach that best fits your application's architecture. The key is to handle the property-to-field conversion explicitly in your form or view code.