django-cbv-formpreview 0.2.0a1

Django's FormPreview updated to use class based views.

Usage

I will write better documentation shortly, but for now see Django’s documentation on its version of this class.

This project is just a fork Django’s FormPreview class. There are a few basic differences when using django-cbv-formpreview’s version of the class:

1. Specify the form you wish to use by setting form_class on your subclass. This is instead of constructing a FormPreview with the form class (i.e. don’t do MyFormPreview(MyForm))

2. Include it in your URLconf just as you would a normal class-based view (i.e. MyFormPreview.as_view())

3. You still need to override the done method, but it only takes a cleaned form as an argument. Django’s version takes an HttpRequest object and the form’s cleaned_data. Like all class-based views, the current HttpRequest is available as an instance attribute (i.e. self.request).

4. The process_preview method is still there, but it takes a form and the context it will pass to the template. It is no longer passed an HttpRequest object for the same reason as above.

Along with the above backwards incompatibile changes that affect publicly documented behavior, a comment in the source code suggested a few methods that might be useful to override. The methods get_initial, security_hash, and failed_hash used to take an HttpRequest as an argument but no longer do for the same reason stated above. A few other changes to note:

• process_params has been removed. The args and kwargs passed to the view are available as instance attributes with the same names. If you need to do something with them before the view is processed, override dispatch and be sure to return a call to the parents dispatch method (i.e. return super(MyFormPreview, self).dispatch(request, *args, **kwargs).

• get_auto_id has also been removed. Override get_form_kwargs if you need it.

Please let me know if I’ve missed anything.

Background

The FormPreview class from the contrib.formtools app is a class based view that’s been in Django for over 5 years. Originally written by Adrian Holovaty, it hasn’t changed significantly since its release.

Starting in version 1.3, Django has a “blessed” version of class based views. This package contains an updated version of FormPreview that inherits from the new FormView class. This enables a consistent API for class based views in Django. Of particular use are the methods provided by the FormMixin class, from which FormView inherits. For example, the get_form method gives you control over the instantiation of the form class. This allows you to construct an instance with non-standard arguments which was the original motivation of the patch.

I originally strove for backwards compatibility but after using this in production, decided it wasn’t worth it. The final straw was when I needed to call the save method on a form in done. Django’s FormPreview only passed cleaned_data and I didn’t want to reconstruct the form as recleaning it would unnecessarily hit the database.

I previously filed a ticket on Django’s trac to include the original backwards compatibile version of django-cbv-formpreview in Django 1.4. Now that I’ve broken backwards compatibility, I’m not sure how the core devs will respond to it. I personally feel that few people actually use this functionality and would therefore have minimal impact on the community.