django-secretballot 0.3.0

===================
django-secretballot
===================

Django voting application that allows voting without a logged in user.

Provides abstract base model for types that the user wishes to allow voting on as well as related utilities including generic views to ease the addition of 'anonymous' voting to a Django project.

django-secretballot is a project of Sunlight Labs (c) 2009.
Written by James Turk <jturk@sunlightfoundation.com>

Source: http://github.com/sunlightlabs/django-secretballot/

Requirements
============

python >= 2.4

django >= 1.0


Usage
=====

settings.py
-----------

* add ``secretballot`` to INSTALLED_APPS
* add a secretballot middleware to MIDDLEWARE_CLASSES (see middleware section for details)

Enabling voting for models
--------------------------

In order to attach the voting helpers to a particular model it is enough to call ``secretballot.enable_voting_on`` passing the model class.

For example::

from django.db import models
import secretballot

class Story(models.Model):
title = models.CharField(max_length=100)
description = models.CharField(max_length=200)
timestamp = models.DateTimeField()
...

secretballot.enable_voting_on(Story)

Using voting-enabled models
---------------------------

Once a model is 'voting-enabled' a number of special fields are available on all instances:

Fields
~~~~~~

votes:
Manager to of all ``Vote`` objects related to the current model (typically doesn't need to be accessed directly)
(can be renamed by passing ``votes_name`` parameter to ``enable_voting_on``)
total_upvotes:
Total number of +1 votes
(can be renamed by passing ``upvotes_name`` parameter to ``enable_voting_on``)
total_downvotes:
Total number of -1 votes
(can be renamed by passing ``downvotes_name`` parameter to ``enable_voting_on``)
vote_total:
shortcut accessor for (total_upvotes-total_downvotes)
(can be renamed by passing ``total_name`` parameter to ``enable_voting_on``)
_secretballot_enabled
boolean indicating that secretballot is enabled (can be tested for with hasattr)
(cannot be renamed, exists for a reliable check that secretballot is available even if all
other fields were renamed)

Functions
~~~~~~~~~

add_vote:
function that takes a token and a vote (+1 or -1) and adds or updates the vote for said token
(can be renamed by passing ``add_vote_name`` parameter to ``enable_voting_on``)
remove_vote:
function that takes a token and removes the vote (if present) for said token
(can be renamed by passing ``remove_vote_name`` parameter to ``enable_voting_on``)

Manager
~~~~~~~

A special manager is added that enables the inclusion of ``total_upvotes`` and ``total_downvotes`` as well as some extra functionality.

This manager by default replaces the ``objects`` manager, but this can be altered by passing the ``manager_name`` parameter to ``enable_voting_on``.

There is also an additional method on the Votable manager:

from_request(self, request):
When called on a votable object's queryset will add a ``user_vote`` attribute that is the vote cast by the current 'user' (actually the token assigned to the request)

For example::

def story_view(request, slug):
story = Story.objects.from_request(request).get(pk=slug)
# story has the following extra attributes
# user_vote: -1, 0, or +1
# total_upvotes: total number of +1 votes
# total_downvotes: total number of -1 votes
# vote_total: total_upvotes-total_downvotes
# votes: related object manager to get specific votes (rarely needed)


tokens and SecretBallotMiddleware
---------------------------------

Without user logins it is impossible to be certain that a user does not vote more than once, but there are several methods to limit abuses. secretballot takes a fairly hands-off approach to this problem, the Vote object has a ``token`` field that is used to store a uniquely identifying token generated from a request. To limit how many votes come from a particular ip address it is sufficient to set the token to the IP address, but it is also possible to develop more sophisticated heuristics to limit voters.

secretballot uses a simple piece of middleware to do this task, and makes it trival for users to define their own middleware that will use whatever heuristic they desire.

SecretBallotMiddleware is an abstract class that defines a generate_token(request) method that should return a string to be used for the token.

For convinience several middleware have already been defined:

SecretBallotIpMiddleware:
simply sets the token to request.META['REMOTE_ADDR'] -- the user's IP address
SecretBallotIpUseragentMiddleware:
sets the token to a hash of the user's ip address and user agent -- hopefully slightly more unique than IP alone

If you wish to define your own middleware simply derive a class from SecretBallotMiddleware and implement the generate_token method. If you come up with something that may be useful for others contributions are always welcome.

Generic Views
-------------

``secretballot.views`` includes the following generic views::

vote(request, content_type, object_id, vote,
redirect_url=None, template_name=None, template_loader=loader,
extra_context=None, context_processors=None, mimetype=None)

This view creates or alters a vote on the object of ``content_type`` with a primary key of ``object_id``.
If a vote already exists it will be replaced (unless vote is 0 in which case it will be deleted).

The ``token`` attribute of the vote that is used to prevent unlimited voting is set within this view based on the active SecretBallotMiddleware.

Depending on the parameters given the return value of this view varies:

#. if redirect_url is specified it will be used no matter what
#. if template_name is specified it will be used (along with template_loader, context_processors, etc.)
#. without redirect_url or template_name a text/json response will be returned

content_type:
Class that voting is taking place on (a VotableModel-derived model)
May be an instance of ``django.contrib.contenttypes.models.ContentType``,
the Model class itself, or an "app.modelname" string.
object_id:
primary key of object to vote on
vote:
value of this vote (+1, 0, or -1) (0 deletes the vote)
can_vote_test:
(optional) function that allows limiting if user can vote or not (see ``can_vote_test``)
redirect_url:
(optional) url to redirect to, if present will redirect instead of returning a normal HttpResponse
template_name:
(optional) template to render to, recieves a context containing ``content_obj`` which is the object voted upon
template_loader:
(optional) template loader to use, defaults to ``django.template.loader``
extra_context:
(optional) dictionary containing any extra context, callables will be called at render time
context_processors:
(optional) list of context processors for this view
mimetype:
(optional) mimetype override


can_vote_test
~~~~~~~~~~~~~

can_vote_test is an optional argument to the view that can be specified in the urlconf that is called before a vote is recorded for a user

Example implementation of can_vote_test::

def only_three_votes(request, content_type, object_id, vote):
return Vote.objects.filter(content_type=content_type, token=request.secretballot_token).count() < 3

All can_vote_test methods must take the non-optional parameters to ``secretballot.views.vote`` and should return True if the vote should be allowed. If the vote is not allowed by default the view will return a 403, but it is also acceptable to raise a different exception.