Render dropdown in django view using values from postgres arrayfield

Here is an example from the model:

class Shipment(models.Model):
    shipment_id = models.BigAutoField(null=False, primary_key=True)
    potential_shipping_dates = ArrayField(models.DateField(), verbose_name='Ship Dates', null=True)

Here is what I'm sort of attempting in my form:

class ShippingForm(forms.Form):
    potential_shipping_dates = forms.ModelChoiceField(queryset=Shipment.objects.all())
    def __init__(self, *args, **kwargs):
        super(ShippingForm, self).__init__(*args, **kwargs)

And here is where my form is added to context:

context['shippingForm'] = ShippingForm(initial=??what_goes_here_maybe??)

My form renders fine but I want to show a dropdown with a date for each option.

Okay this is a bit complex, but I think I understand what you're trying to do, and where you're going wrong.

So you have a Shipment model, and each Shipment instance has a field with a few different potential_shipping_dates.

Say you have 2 shipments:

IN : ship1 = Shipment.objects.first()
OUT:

IN : ship1.potential_shipping_dates
OUT: ['01/01/2021', '02/02/2021']

IN : ship2 = Shipment.objects.last()
OUT:

IN : ship2.potential_shipping_dates
OUT: ['03/03/2021', '04/04/2021']

Now, do you want the dropdown to have all 4 dates as possibilities, and that will select the Shipment?

Or do you want to select a date after selecting the shipment in the form?

^^ Answered in comments

Okay so you will need to pass the instance through to the form:

views.py

# Inherit from Django's UpdateView to have `instance` passed through to the form
class ShippingFormView(UpdateView):
    model = Shipment
    form_class = ShippingForm


# Or if you don't want to inherit from inherit from UpdateView
class ShippingFormView(Blah):
    model = Shipment
    form_class = ShippingForm

    def get_form_kwargs(self):
        kwargs = super().get_form_kwargs()
        kwargs['instance'] = self.get_object()
        return kwargs


# Or if you're using function based views
def shipping_form_view(request, pk):
    shipment = get_object_or_404(Shipment, pk=pk)
    form = ShippingForm(request, instance=shipment)
    ...

forms.py

class ShippingForm(forms.Form):
    potential_shipping_dates = forms.ChoiceField(choices=[])

    def __init__(self, *args, instance, **kwargs):
        super(ShippingForm, self).__init__(*args, **kwargs)
        self.fields['potential_shipping_dates'].choices = ((dt, dt) for dt in instance.potential_shipping_dates)

ModelChoiceFields are used when selecting an object, not an attribute on one.