django-querysetsequence 0.10

Supported Features

Listed below are features of Django’s QuerySets that QuerySetSequence implements. The behavior should match that of QuerySet, but applied across multiple QuerySets:

• Methods that take a list of fields (e.g. filter(), exclude(), get(), order_by()) must use fields that are common across all sub-QuerySets.

• Relationships across related models work (e.g. 'foo__bar', 'foo', or 'foo_id'). syntax).

• The sub-QuerySets are evaluated as late as possible (e.g. during iteration, slicing, pickling, repr()/len()/list()/bool() calls).

• Public QuerySet API methods that are untested/unimplemented raise NotImplementedError.

Requirements

• Python (2.7, 3.4, 3.5, 3.6)

• Django (1.11, 2.0)

• (Optionally) Django REST Framework (3.4, 3.5, 3.6, 3.7)

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']

Django REST Framework integration

django-querysetsequence comes with a custom CursorPagination class that helps integration with Django REST Framework. It is optimized to iterate over a QuerySetSequence first by QuerySet and then by the normal ordering configuration. This uses the optimized code-path for iteration that avoids interleaving the individual QuerySets. For example:

from queryset_sequence.pagination import SequenceCursorPagination

class PublicationPagination(SequenceCursorPagination):
    ordering = ['author', 'title']

class PublicationViewSet(viewsets.ModelViewSet):
    pagination_class = PublicationPagination

    def get_queryset(self):
        # This will return all Books first, then all Articles. Each of those
        # is individually ordered by ``author``, then ``title``.
        return QuerySetSequence(Book.objects.all(), Article.objects.all())

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.