Display update form in a modal with initial data

mixins.py

from django.views import generic
from django.db.models.base import Model
from collections import OrderedDict
from django.forms import BaseForm
from django.core.validators import RegexValidator

__all__ = (
    'AdditionalFormsMixin',
)


class AdditionalFormsManager(OrderedDict):
    # Allow only these chars to be able to call them as variables in the
    # template.
    _name_validator = RegexValidator(
        regex=r'^\w+$', message='Form name contains unsupported characters'
    )

    def register_form(self, name: str, form_class: BaseForm, action_url: str,
                      is_multipart: bool=False,
                      model_instance: Model=None) -> None:
        """
        Register a form with the manager

        The name is validated to be useful as template variable and a
        ValiditionError is raised if this is not the case.

        :param name: form name, used as variable in the context
        :param form_class: class of the form to add to the context
        :param action_url: url the form should be submitted to
        :param is_multipart: if the form should be capable of uploading files
        :param model_instance: if the form is a model form used for update,
        it will update this instance.
        """
        self._name_validator(name)
        formdata = {
            'form_class': form_class,
            'action_url': action_url,
            'is_multipart': is_multipart,
            'model_instance': model_instance,
        }
        self[name] = formdata

    def get_additional_form(self, name: str) -> tuple:
        try:
            formdata = self.get(name)
        except KeyError:
            raise KeyError('No form with name {} found.'.format(name))
        form_class = formdata.pop('form_class')
        instance = formdata.pop('model_instance')
        form = form_class(instance=instance) if instance else form_class()
        return form, formdata

    def get_context_update(self) -> dict:
        update = {}
        for name in self.keys():
            form, data = self.get_additional_form(name)
            update[name] = form
            for prop in data:
                propname = '{}__{}'.format(name, prop)
                update[propname] = data[prop]

        return update


class AdditionalFormsMixin(generic.base.ContextMixin):
    def __init__(self, *args, **kwargs):
        self._afm = AdditionalFormsManager()
        super().__init__(*args, **kwargs)

    def add_additional_form(self, name: str, form_class: BaseForm,
                            action_url: str, **kwargs) -> None:
        """
        Convenience proxy to `AdditionalFormsManager.register_form()`.
        Also forwards-compatible with any additional keyword arguments it may
        choose to support.

        :param name: form name, used as variable in the context
        :param form_class: class of the form to add to the context
        :param action_url: url the form should be submitted to
        """
        self._afm.register_form(name, form_class, action_url, **kwargs)

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context.update(self._afm.get_context_update())
        return context

project.html

{% extends "base.html" %}
{% load l10n bootstrap3 %}
{% block form_media %}{{ project_update_form.media }}{% endblock %}
{% block content %}
	{# deleted for brevity #}
	<nav class="col-md-2 col-md-offset-1" role="navigation">
		<ul class="nav nav-stacked nav-pills">
			<li role="presentation">
				<a href="#project-update" data-toggle="modal">Edit</a>
			</li>
		</ul>
	</nav>
	<div class="modal fade" id="project-update">
		<div class="modal-dialog">
			<div class="modal-content">
				<form class="form-horizontal" action="{{ project_update_form__action_url }}" method="post">
					{% csrf_token %}
					<div class="modal-header">
						<button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
						<h4 class="modal-title">Edit project</h4>
					</div>
					<div class="modal-body">
						{% bootstrap_form project_update_form layout="horizontal" %}
					</div>
					<div class="modal-footer">
						<button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
						<button type="submit" class="btn btn-primary">Save changes</button>
					</div>
				</form>
			</div><!-- /.modal-content -->
		</div><!-- /.modal-dialog -->
	</div><!-- /.modal -->
{% endblock %}

views.py

from django.views import generic
from django.utils.translation import ugettext_lazy as _
from .. import models, forms
from .mixins import AdditionalFormsMixin
from django.urls import reverse


class ProjectDetailView(AdditionalFormsMixin, generic.DetailView):
    model = models.Project
    context_object_name = 'project'
    template_name = 'view/project.html'

    def get(self, request, *args, **kwargs):
        instance = self.get_object()
        url = reverse('project_edit', kwargs={'slug': instance.slug})
        self.add_additional_form(
            'project_update_form', forms.ProjectForm, url,
            model_instance=instance
        )
        return super().get(request, *args, **kwargs)