aidsoid/django-next-prev

Django utility to retrieve the next or previous object, given a current object and a queryset.

Purpose

django-next-prev provides utilities to get the next or previous item within an ordered, filtered queryset. For example, you could display a link to the next featured post on a post detail page, or show chronological next and previous links for all published posts.

Installation

Download the source from https://pypi.python.org/pypi/django-next-prev/ and run python setup.py install, or:

> pip install django-next-prev

Django 1.8 or higher is required.

Quick start

Given this models.py:

from django.db import models

class Category(models.Model):
    title = models.CharField(max_length=100)

class Post(models.Model):
    title = models.CharField(max_length=100)
    category = models.ForeignKey(Category, on_delete=models.CASCADE)
    created = models.DateField()
    featured = models.BooleanField(default=False)
    text = models.TextField()

    class Meta:
        # order on primary key to make sure it's unique
        ordering = ('created', 'title', 'pk')

You can do the following

from next_prev import next_in_order, prev_in_order
from .models import Post

# default ordering
first = Post.objects.first()
second = next_in_order(first)
prev_in_order(second) == first # True
last = prev_in_order(first, loop=True)

# custom ordering
qs = Post.objects.all().order_by('-created', '-pk')
newest = qs.first()
second_newest = next_in_order(newest, qs=qs)
oldest = prev_in_order(newest, qs=qs, loop=True)

# filtered
qs = Post.objects.filter(featured=True)
first_featured = qs.first()
second_featured = next_in_order(first_featured, qs=qs)

Ordering considerations

Order fields must be non-nullable.

If results are inconsistent with the order of your queryset, you're probably ordering on a non-unique combination of fields. For example, ordering = ('sort_order', ) with the duplicate sort_order values. To resolve this, add a unique field to your ordering, i.e. ordering = ('sort_order', 'pk')