drf-cached-instances 0.3.4

Cached instances for Django REST Framework

Speed up Django REST Framework (DRF) reads by storing instance data in cache.

This code was split from browsercompat. You may be interested in viewing the browsercompat source code for a full example implementation.

• Code: https://github.com/jwhitlock/drf-cached-instances

• Free software: Mozilla Public License Version 2.0

• Documentation: https://drf-cached-instances.readthedocs.io

How it works

In a normal DRF view, a Django queryset is used to load an object or list of objects. A serializer is used to convert the objects into the “native” representation, and then a renderer works on this native representation. If the serializer includes data from related models, then multiple database queries may be required to generate a native representation. Some database efficiency can be gained by using select_related, but a minimum of one query is needed, which is unfortunate for an API with heavy read usage.

This project replaces the Django queryset with a cache-aware proxy class, making it possible to serve a read request with zero database requests (to retrieve an instance) or one request (to get the primary keys for a list view). It is suitable for APIs with heavy read operations and lots of linking between related instances.

When using the cache, Django objects are serialized to JSON. Only the attributes needed for the DRF native representation are stored in the cache. This include the JSON representation of fields such as foreign keys, reverse relations, and dates and times. These serialized objects are stored by primary key in the cache. When an instance is found in the cache, no database reads are needed to render the DRF representation. If the instance is not in the cache, it is serialized and stored, so that future reads will be faster.

The API implementor writes methods to handle JSON serialization, loading from the database, and identifying invalid cache entries on changes. There are a few integration points, including a mixin for views to load data from the cache. With only a few changes to existing code, your read views could be a lot faster.

Project status

This code is used for the browsercompat project, which was developed from 2015 - 2016, but is on hold as of August 2016. Since this was the primary user of this code, it may be a while before more features are implemented.

History

0.3.4 (2016-08-14)

• Drop support for Django 1.7, Python 2.6

• Expand tests to Django 1.10, Django REST Framework 3.4, Python 3.5

0.3.3 (2015-11-05)

• Add serializer for datetime.timedelta, to support Django 1.8’s DurationField (creynold)

• Convert string representations of datetimes, dates, and timedeltas

• Expand tests to Django 1.9 beta 1 and Django REST Framework 3.3

0.3.2 (2015-09-23)

• Remove deprecation warning in Django 1.8

• Expand tests to Django master and Django REST Framework 3.2

• Fix invalid mock.patch tests that break under mock 1.3.0

• Documentation updates and fixes

0.3.1 (2015-06-16)

• Move get_object_or_404 to mixin method, to allow easier extending.

0.3.0 (2015-04-09)

• Tested with Django 1.8

• Tested with Django REST Framework 2.4, 3.0, and 3.1

• CachedModel now supports .pk attribute as an alias, usually to the .id field. DRF 3 uses .pk to determine if a model is saved to database, and returns empty relation data for unsaved fields.

• cache.delete_all_versions() will delete all cached instances of a model and PK. This is useful when changes are made outside of normal requests, such as during a data migration.

0.2.0 (2014-12-11)

• Add update_only option to cache.update_instance, to support eventual consistency for cold caches.

0.1.0 (2014-11-06)

• First release on PyPI.