Django NumberedModel

A Django model for objects that are numbered sequentially

Introduction

This app was inspired by django-ordered-model and other similar apps. It overrides the save() and delete() methods to automatically renumber all objects upon save and delete events. Admin integration comes naturally, as users simply see a "Number" field that they can use to reorder the objects. Using NumberedModel as the base model is ideally suited for stuff like todo-lists, assignments, rankings, etc.

Installation

Django NumberedModel is not (yet!) installable via package managers such as apt or pip. Simply clone this repository and run python setup.py install. You can also copy the numberedmodel directory into your own Django project.

Configuration

First, add numberedmodel to your INSTALLED_APPS (in setup.py):

INSTALLED_APPS += ['numberedmodel']

Second, inherit your own model from numberedmodel.NumberedModel (in models.py):

from django import models
from numberedmodel import NumberedModel

class Assignment(NumberedModel):
    number = models.PositiveIntegerField(blank=True)
    content = models.TextField()

    class Meta:
        ordering = ['number']

How does NumberedModel know which field is the number field? Well, it look at the first entry in the ordering list, so make sure this is set to an integer-type field. If you specify blank=True for this field (as in the example), users are allowed to leave the field blank, in which case NumberedModel assigns the last number upon saving the object.

Third, create and run the database migrations:

$ ./manage.py makemigrations
$ ./manage.py migrate

Subset ordering

By default, NumberedModel renumbers all objects upon saving. In some cases, however, only renumbering of a certain subset is required. When a model contains a ForeignKey field, for instance, you probably want the numbers to be sequential with respect to the foreign object. For this, create a method called number_with_respect_to that returns a QuerySet. Example:

from django import models
from numberedmodel import NumberedModel

class Person(models.Model):
    name = models.CharField(max_length=255)

class Task(NumberedModel):
    number = models.PositiveIntegerField(blank=True)
    content = models.TextField()
    person = models.ForeignKey(Person, related_name='tasks')

    class Meta:
        ordering = ['number']

    def number_with_respect_to(self):
        return self.person.tasks.all()