django-querysetsequence 0.2.2

Chain together multiple (disparate) QuerySets to treat them as a single QuerySet.

The QuerySetSequence wrapper helps to deal with disparate QuerySet classes, while treating them as a single QuerySet.

Supported Features

• filter() / exclude() / get() across fields common to all sub-QuerySets.

• order_by() fields common across all sub-QuerySets.

• len() / count() to get the total length across all QuerySets.

• Slicing and indexing works as expected.

• QuerySetSequence is an iterable.

• QuerySets are evaluated as late as possible.

Known Issues

• Cannot handle order_by() when fields include other models (e.g. ForeignKeys).

• The fully QuerySet API is not complete.

Installation

Install the package using pip.

pip install --upgrade django-querysetsequence

Usage

# Import QuerySetSequence
from queryset_sequence import QuerySetSequence

# Create QuerySets you want to chain.
from .models import SomeModel, OtherModel

# Chain them together.
query = QuerySetSequence(SomeModel.objects.all(), OtherModel.objects.all())

# Use query as if it were a QuerySet! E.g. in a ListView.

Example

class Author(models.Model):
    name = models.CharField(max_length=50)

    class Meta:
        ordering = ['name']

    def __str__(self):
        return self.name


class Article(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author)

    def __str__(self):
        return "%s by %s" % (self.title, self.author)


class Book(models.Model):
    title = models.CharField(max_length=50)
    author = models.ForeignKey(Author)
    release = models.DateField(auto_now_add=True)

    def __str__(self):
        return "%s by %s" % (self.title, self.author)

# Create some data.
alice = Author.objects.create(name='Alice')
article = Article.objects.create(title='Dancing with Django', author=alice)

bob = Author.objects.create(name='Bob')
article = Article.objects.create(title='Django-isms', author=bob)
article = Book.objects.create(title='Biography', author=bob)

# Create some QuerySets.
books = Book.objects.all()
articles = Article.objects.all()

# Combine them into a single iterable.
published_works = QuerySetSequence(books, articles)

# Find Bob's titles.
bob_works = published_works.filter(author=bob)
# Still an iterable.
print([w.title for w in bob_works])  # prints: ['Biography', 'Django-isms']

# Alphabetize the QuerySet.
published_works = published_works.order_by('title')
print([w.title for w in published_works])  # prints ['Biography', 'Dancing with Django', 'Django-isms']

Attribution

This is based on a few DjangoSnippets that had been going around:

• Originally from https://www.djangosnippets.org/snippets/1103/

• Modified version from https://djangosnippets.org/snippets/1253/

• Upgraded version from https://djangosnippets.org/snippets/1933/

• Updated version from django-ko-demo from The Atlantic

Contribute

• Check for open issues or open a fresh issue to start a discussion around a feature idea or a bug.

• Fork the repository on GitHub to start making your changes.

• Write a test which shows that the bug was fixed or that the feature works as expected.

• Send a pull request and bug the maintainer until it gets merged and published.