Question

I need an integer form field to have a ‘default’ value. But I need to define this value at runtime.

I do it like ths:

# at my form constructor:
def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None, initial=None, error_class=ErrorList,
             label_suffix=':', empty_permitted=False):
    super(FlatSearchForm, self).__init__(data, files, auto_id, prefix, initial, error_class, label_suffix,
        empty_permitted)

    min_price = ... # some code to find the minimum price
    self.price_min = min_price # will be used later

    max_price = ... # some code to find the maximum price
    self.price_max = max_price

    # here we go:
    self.fields['price_from'] = forms.IntegerField(min_value=min_price, max_value=max_price, initial=min_price)
    self.fields['price_to'] = forms.IntegerField(min_value=min_price, max_value=max_price, initial=max_price)

# ...
# how I use the form (in views.py):
class SearchFlatView(ListView):
    model = Flat
    context_object_name = 'flats'
    template_name = 'catalog/search.html'

    def get_context_data(self, **kwargs):
        context = super(SearchFlatView, self).get_context_data(**kwargs)
        context['form'] = FlatSearchForm(self.request.GET)
        return context

The problem is: values are not shown in the form when I render the field using {{form.price_from}} and {{form.price_to}} – these fields are just empty!

Can you please tell me what I am doing wrong?

Answer 1

You cannot set dynamically initial values for fields in a bound form. See the docs: https://docs.djangoproject.com/en/dev/ref/forms/fields/#initial

The initial argument lets you specify the initial value to use when
rendering this Field in an unbound Form.

What you can do however is to create an unbound form, with still preserving the request.GET params:

initial = request.GET.copy()
initial['price_from'] = some_min_price
initial['price_to'] = some_max_price
context['form'] = FlatSearchForm(initial=initial)

While in the form __iniit__ you’ll have:

def __init__(self, *args, **kwargs):
    super(Form, self).__init__(*args, **kwargs)
    initial = kwargs.get("initial", {})
    default_min_value = ... #  some default value in case there is no `initial` passed
    default_max_value = ...
    self.fields['price_from'] = forms.IntegerField(min_value=initial.get('min_value', default_min_value), max_value=initial.get('max_value', default_max_value))
    self.fields['price_to'] = forms.IntegerField(min_value=initial.get('min_value', default_min_value), max_value=initial.get('max_value', default_max_value))

Or you may want to change this logic, if needed.