django-limits 0.0.6

Defining a Limiter class

To properly limit your models, you need a limiter class. This isn’t auto loaded, so it can be anywhere, should probably go in a limiter.py file or in your models.py.

All limiters inherit from the django_limits.limiter.Limiter, but you can override most of this class as needed.

The simplest limiter, is just an inheritance of this class, with a class attribute defining the limiting rules. A set of rules is a dictionary, with the key being a model class, and the associated values being a dictionary described below, or list of dictionaries, like so:

from django_limits.limiter import Limiter
from django.contrib.auth.models import User

class MyLimiter(Limiter):
    rules = {
        User: [
            {
                'limit': 20,
                'message': "Only 20 active users allowed",
                'filterset': Q(is_active=True)
            },
            {
                'limit': 10,
                'message': "Only 10 staff members allowed",
                'filterset': Q(is_staff=True)
            }
        ]
    }

The above Limiter will only allow a maximum of 20 active users, and 10 staff members.

Defining a rules dictionary

A rules dictionary can contain the following keys:

• limit (required - The total number of the given model allowed, or if there is a queryset, the total allowed for that queryset

• message - The message shown when a user tries to exceed this number

• filterset - A django Q filters that defines the types of models to restrict on, if this is not set the total number of the model in the database is used (e.g Model.objects.all())

• template - The template used to render the page explaining the limit restriction, defaults to django_limits/limit_exceeded.html

An example rule is below for a widget is below:

Widget: [
    {
        'limit': 10,
        'message': "Only 10 staff members allowed",
        'filterset': Q(color="Blue")
    },
    {
        'limit': 10,
        'message': "Only 10 staff members allowed",
        'filterset': Q(color="Red")
    },
    {
        'limit': 30,
        'message': "Only 30 widgets allowed",
        'template': "widgets/totla_widgets_exceeded.html'
    }
]

In this example, at most 10 blue, 10 red and a total 30 widgets are allowed.

How it works

Django limtis installs a pre_save signal for every model, and checks against the rules, and to prevent the save from finishing throws a LimitExceeded exception which is caught by the middleware, which in turn renders a page with a HTTP 403 error.

Apologies to Tina Turner.