https://github.com/roverdotcom/django-delayed-union

A library designed to workaround some drawbacks with Django's union, intersection, and difference operations.
https://github.com/roverdotcom/django-delayed-union

Last synced: about 1 year ago
JSON representation

A library designed to workaround some drawbacks with Django's union, intersection, and difference operations.

• Host: GitHub
• URL: https://github.com/roverdotcom/django-delayed-union
• Owner: roverdotcom
• License: bsd-3-clause
• Created: 2018-03-19T13:52:27.000Z (about 8 years ago)
• Default Branch: master
• Last Pushed: 2022-01-12T19:09:55.000Z (over 4 years ago)
• Last Synced: 2025-03-26T21:46:06.703Z (about 1 year ago)
• Language: Python
• Homepage:
• Size: 80.1 KB
• Stars: 9
• Watchers: 11
• Forks: 3
• Open Issues: 2
• Metadata Files:
  • Readme: README.rst
  • Changelog: CHANGELOG.rst
  • Contributing: CONTRIBUTING.rst
  • License: LICENSE

Awesome Lists containing this project

README

          
========

Overview

========

.. start-badges

.. list-table::

    :stub-columns: 1

    * - docs

      - |docs|

    * - tests

      - | |travis|

        | |codecov|

    * - package

      - | |version| |wheel| |django-versions| |supported-versions|

        | |commits-since|

.. |docs| image:: https://readthedocs.org/projects/django-delayed-union/badge/?style=flat

    :target: https://readthedocs.org/projects/django-delayed-union

    :alt: Documentation Status

.. |travis| image:: https://travis-ci.org/roverdotcom/django-delayed-union.svg?branch=master

    :alt: Travis-CI Build Status

    :target: https://travis-ci.org/roverdotcom/django-delayed-union

.. |codecov| image:: https://codecov.io/github/roverdotcom/django-delayed-union/coverage.svg?branch=master

    :alt: Coverage Status

    :target: https://codecov.io/github/roverdotcom/django-delayed-union

.. |version| image:: https://img.shields.io/pypi/v/django-delayed-union.svg

    :alt: PyPI Package latest release

    :target: https://pypi.python.org/pypi/django-delayed-union

.. |commits-since| image:: https://img.shields.io/github/commits-since/roverdotcom/django-delayed-union/v0.1.7.svg

    :alt: Commits since latest release

    :target: https://github.com/roverdotcom/django-delayed-union/compare/v0.1.7...master

.. |wheel| image:: https://img.shields.io/pypi/wheel/django-delayed-union.svg

    :alt: PyPI Wheel

    :target: https://pypi.python.org/pypi/django-delayed-union

.. |supported-versions| image:: https://img.shields.io/pypi/pyversions/django-delayed-union.svg

    :alt: Supported versions

    :target: https://pypi.python.org/pypi/django-delayed-union

.. |django-versions| image:: https://img.shields.io/pypi/djversions/django-delayed-union.svg

   :alt: Django versions

   :target: https://pypi.python.org/pypi/django-delayed-union

.. end-badges

``django-delayed-union`` is library designed to workaround some

drawbacks with Django's union, intersection, and difference

operations.  In particular, once one of these operations is performed,

certain methods on the queryset will silently not work::

  >>> qs = User.objects.filter(id=1)

  >>> unioned_qs = qs.union(qs)

  >>> should_be_empty_qs = unioned_qs.exclude(id=1)

  >>> user, = list(should_be_empty_qs); user.id

  1

In order to work around this, ``django-delayed-union`` provides

wrappers around a collection of querysets.  These wrappers implement a

similar interface to ``QuerySet``, and delay performing the union,

intersection, or difference operations until they are needed::

  >>> from django_delayed_union import DelayedUnionQuerySet

  >>> qs = User.objects.filter(id=1)

  >>> unioned_qs = DelayedUnionQuerySet(qs, qs)

  >>> empty_qs = unioned_qs.exclude(id=1)

  >>> list(empty_qs)

  []

Operations which would typically return a new ``QuerySet`` instead

return a new ``DelayedQuerySet`` with the operation applied to its

collection of querysets.

One example of where this code has been useful with is when the the

MySQL query planner has chosen an inefficient query plan for the

queryset of a `Django REST Framework `_ view

which used an ``OR`` condition.  By using ``DelayedUnionQuerySet``,

subclasses could perform additional filters on the queryset while

still maintaining the efficient query plan.

* Free software: BSD 3-Clause License

Installation

============

::

    pip install django-delayed-union

Documentation

=============

https://django-delayed-union.readthedocs.io/

Development

===========

To run the all tests run::

    tox