[Django]-Making a Django form class with a dynamic number of fields

Here’s another option: how about a formset?
Since your fields are all the same, that’s precisely what formsets are used for.

The django admin uses FormSets + a bit of javascript to add arbitrary length inlines.

class ColorForm(forms.Form):
    color = forms.ChoiceField(choices=(('blue', 'Blue'), ('red', 'Red')))

ColorFormSet = formset_factory(ColorForm, extra=0) 
# we'll dynamically create the elements, no need for any forms

def myview(request):
    if request.method == "POST":
        formset = ColorFormSet(request.POST)
        for form in formset.forms:
            print "You've picked {0}".format(form.cleaned_data['color'])
    else:
        formset = ColorFormSet()
    return render(request, 'template', {'formset': formset}))

JavaScript

    <script>
        $(function() {
            // this is on click event just to demo.
            // You would probably run this at page load or quantity change.
            $("#generate_forms").click(function() {
                // update total form count
                quantity = $("[name=quantity]").val();
                $("[name=form-TOTAL_FORMS]").val(quantity);  

                // copy the template and replace prefixes with the correct index
                for (i=0;i<quantity;i++) {
                    // Note: Must use global replace here
                    html = $("#form_template").clone().html().replace(/__prefix_/g', i);
                    $("#forms").append(html);
                };
            })
        })
    </script>

Template

    <form method="post">
        {{ formset.management_form }}
        <div style="display:none;" id="form_template">
            {{ formset.empty_form.as_p }}
        </div><!-- stores empty form for javascript -->
        <div id="forms"></div><!-- where the generated forms go -->
    </form>
    <input type="text" name="quantity" value="6" />
    <input type="submit" id="generate_forms" value="Generate Forms" />

you can do it like

def __init__(self, n,  *args, **kwargs):
  super(your_form, self).__init__(*args, **kwargs)
  for i in range(0, n):
    self.fields["field_name %d" % i] = forms.CharField()

and when you create form instance, you just do

forms = your_form(n)

it’s just the basic idea, you can change the code to whatever your want. 😀

The way I would do it is the following:

1. Create an “empty” class that inherits from froms.Form, like this:

   class ItemsForm(forms.Form):
       pass
   

2. Construct a dictionary of forms objects being the actual forms, whose composition would be dependent on the context (e.g. you can import them from an external module). For example:

   new_fields = {
       'milk'  : forms.IntegerField(),
       'butter': forms.IntegerField(),
       'honey' : forms.IntegerField(),
       'eggs'  : forms.IntegerField()}
   

3. In views, you can use python native “type” function to dynamically generate a Form class with variable number of fields.

   DynamicItemsForm = type('DynamicItemsForm', (ItemsForm,), new_fields)
   

4. Pass the content to the form and render it in the template:

   Form = DynamicItemsForm(content)
   context['my_form'] = Form
   return render(request, "demo/dynamic.html", context)
   

The “content” is a dictionary of field values (e.g. even request.POST would do).
You can see my whole example explained here.

Another approach: Rather than breaking the normal field initialization flow, we can override fields with a mixin, return an OrderedDict of dynamic fields in generate_dynamic_fields which will be added whenever its set.

from collections import OrderedDict

class DynamicFormMixin:
    _fields: OrderedDict = None

    @property
    def fields(self):
      return self._fields

    @fields.setter
    def fields(self, value):
        self._fields = value
        self._fields.update(self.generate_dynamic_fields())

    def generate_dynamic_fields(self):
        return OrderedDict()

A simple example:

class ExampleForm(DynamicFormMixin, forms.Form):
    instance = None

    def __init__(self, instance = None, data=None, files=None, auto_id='id_%s', prefix=None, initial=None,
                 error_class=ErrorList, label_suffix=None, empty_permitted=False, field_order=None,
                 use_required_attribute=None, renderer=None):
        self.instance = instance
        super().__init__(data, files, auto_id, prefix, initial, error_class, label_suffix, empty_permitted, field_order,
                         use_required_attribute, renderer)

    def generate_dynamic_fields(self):
        dynamic_fields = OrderedDict()
        instance = self.instance
        dynamic_fields["dynamic_choices"] = forms.ChoiceField(label=_("Number of choices"),
                                                              choices=[(str(x), str(x)) for x in range(1, instance.number_of_choices + 1)],
                                                              initial=instance.initial_choice)
        return dynamic_fields