Skip to main content
This is a pre-production deployment of Warehouse. Changes made here affect the production instance of PyPI (pypi.python.org).
Help us improve Python packaging - Donate today!

django-counter-field makes it extremely easy to denormalize and keep track of related model counts.

Project Description

It is sometimes useful to cache the total number of objects associated with another object through a ForeignKey relation. For example the total number of comments associated with an article.

django-counter-field makes it easy to denormalize and keep such counters up to date.

Quick start

  1. Install django-counter-field:

    pip install django-counter-field
    
  2. Add “django_counter_field” to your INSTALLED_APPS setting:

    INSTALLED_APPS = (
        ...
        'django_counter_field',
    )
    
  3. Add a CounterField to your model:

    from django_counter_field import CounterField
    
    
    class Article(models.Model):
        comment_count = CounterField()
    
  4. Add the CounterMixin to the related model:

    from django_counter_field import CounterMixin, connect_counter
    
    
    class Comment(CounterMixin, models.Model):
        article = models.ForeignKey(Article)
    
  5. Connect the related foreign key field with the counter field:

    connect_counter('comment_count', Comment.article)
    

Whenever a comment is created the comment_count on the associated Article will be incremented. If the comment is deleted, the comment_count will be automatically decremented.

Overview

Creating a new counter requires three simple steps:

  1. Add a CounterField field to the parent model.
  2. Add the CounterMixin mixin to the child model.
  3. Use connect_counter to connect the child model with the new counter.

Most counters are simple in the sense that you want to count all child objects. Sometimes, however, objects should be counted based on one or several conditions. For example you may not wish to count all comments on an article but only comments that have been approved. You can create conditional counters by providing a third is_in_counter_func argument to connect_counter:

connect_counter(‘comment_count’, Comment.article, lambda comment: comment.is_approved)

The is_in_counter_func function will be called with Comment objects and must return True if the given comment should be counted. It must not concern itself with checking if the comment is deleted or not, django-counter-field does that by default.

Backfilling

Often you will add a CounterField to a model that already has a large number of associated objects. When a counter is created, it’s value is initialized to zero. This value is likely incorrect. django-counter-field provides a couple of management commands that allow you to rebuild the value of a counter:

  1. List all available counters:

    $ python manage.py list_counters

  2. Rebuild a counter using one of the counter names given by list_counters:

    $ python manage.py rebuild_counter <counter_name>

Note: The rebuild_counter management command will only update counters on objects that have at least one child object. For example articles with at least one comment. Articles with no comments will not be updated. This is a conscious limitation; the use cases for such a feature seem very limited, if existent at all.

Documentation

$ pip install Sphinx $ cd docs $ make html Open build/html/index.html
Release History

Release History

This version
History Node

0.3.1

History Node

0.3

History Node

0.2

History Node

0.1

Download Files

Download Files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

File Name & Checksum SHA256 Checksum Help Version File Type Upload Date
django-counter-field-0.3.1.tar.gz (13.5 kB) Copy SHA256 Checksum SHA256 Source Feb 9, 2014

Supported By

WebFaction WebFaction Technical Writing Elastic Elastic Search Pingdom Pingdom Monitoring Dyn Dyn DNS Sentry Sentry Error Logging CloudAMQP CloudAMQP RabbitMQ Heroku Heroku PaaS Kabu Creative Kabu Creative UX & Design Fastly Fastly CDN DigiCert DigiCert EV Certificate Rackspace Rackspace Cloud Servers DreamHost DreamHost Log Hosting