queryset-refactor: Merged to [6250]

git-svn-id: http://code.djangoproject.com/svn/django/branches/queryset-refactor@6339 bcc190cf-cafb-0310-a4f2-bffc1f526a37

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+============
+Form preview
+============
+
+Django comes with an optional "form preview" application that helps automate
+the following workflow:
+
+"Display an HTML form, force a preview, then do something with the submission."
+
+To force a preview of a form submission, all you have to do is write a short
+Python class.
+
+Overview
+=========
+
+Given a ``django.newforms.Form`` subclass that you define, this application
+takes care of the following workflow:
+
+    1. Displays the form as HTML on a Web page.
+    2. Validates the form data when it's submitted via POST.
+       a. If it's valid, displays a preview page.
+       b. If it's not valid, redisplays the form with error messages.
+    3. When the "confirmation" form is submitted from the preview page, calls
+       a hook that you define -- a ``done()`` method that gets passed the valid
+       data.
+
+The framework enforces the required preview by passing a shared-secret hash to
+the preview page via hidden form fields. If somebody tweaks the form parameters
+on the preview page, the form submission will fail the hash-comparison test.
+
+How to use ``FormPreview``
+==========================
+
+    1. Point Django at the default FormPreview templates. There are two ways to
+       do this:
+
+       * Add ``'django.contrib.formtools'`` to your ``INSTALLED_APPS``
+         setting. This will work if your ``TEMPLATE_LOADERS`` setting includes
+         the ``app_directories`` template loader (which is the case by
+         default). See the `template loader docs`_ for more.
+
+       * Otherwise, determine the full filesystem path to the
+         ``django/contrib/formtools/templates`` directory, and add that
+         directory to your ``TEMPLATE_DIRS`` setting.
+
+    2. Create a ``FormPreview`` subclass that overrides the ``done()`` method::
+
+           from django.contrib.formtools import FormPreview
+           from myapp.models import SomeModel
+
+           class SomeModelFormPreview(FormPreview):
+
+               def done(self, request, cleaned_data):
+                   # Do something with the cleaned_data, then redirect
+                   # to a "success" page.
+                   return HttpResponseRedirect('/form/success')
+
+       This method takes an ``HttpRequest`` object and a dictionary of the form
+       data after it has been validated and cleaned. It should return an
+       ``HttpResponseRedirect`` that is the end result of the form being
+       submitted.
+
+    3. Change your URLconf to point to an instance of your ``FormPreview``
+       subclass::
+
+           from myapp.preview import SomeModelFormPreview
+           from myapp.models import SomeModel
+           from django import newforms as forms
+
+       ...and add the following line to the appropriate model in your URLconf::
+
+           (r'^post/$', SomeModelFormPreview(forms.models.form_for_model(SomeModel))),
+
+       Or, if you already have a Form class defined for the model::
+
+           (r'^post/$', SomeModelFormPreview(SomeModelForm)),
+
+    4. Run the Django server and visit ``/post/`` in your browser.
+
+.. _template loader docs: ../templates_python/#loader-types
+
+``FormPreview`` classes
+=======================
+
+A ``FormPreview`` class is a simple Python class that represents the preview
+workflow.  ``FormPreview`` classes must subclass
+``django.contrib.formtools.preview.FormPreview`` and override the ``done()``
+method. They can live anywhere in your codebase.
+
+``FormPreview`` templates
+=========================
+
+By default, the form is rendered via the template ``formtools/form.html``, and
+the preview page is rendered via the template ``formtools.preview.html``.
+These values can be overridden for a particular form preview by setting
+``preview_template`` and ``form_template`` attributes on the FormPreview
+subclass. See ``django/contrib/formtools/templates`` for the default templates.