Package: django-partial-index
django-partial-indexPartial (sometimes also called filtered or conditional) index support for Django.With partial indexes, only some subset of the rows in the table have corresponding index entries.
This can be useful for optimizing index size and query speed, and to add unique constraints for only selected rows.More info on partial indexes:https://www.postgresql.org/docs/current/static/indexes-partial.htmlhttps://sqlite.org/partialindex.htmlPartial indexes now included in DjangoSince the release ofDjango 2.2 LTSin April 2019,
partial indexes are now supported by standard Django.These are calledindex conditionsthere.The django-partial-index package will live on in maintenance mode.It can be useful if you are maintaining a project on and older version of Django, or wish to migrate django-partial-index indexes to Django 2.2 style on your own schedule.Installpip install django-partial-indexRequirements:Django 1.11, 2.0, 2.1 or 2.2,Python 2.7, 3.4, 3.5, 3.6 or 3.7 (as supported by the Django version),PostgreSQL or SQLite database backend. (Partial indexes are not supported on MySQL, and require major hackery on Oracle.)All Python versions which Django supports are also supported by this package. These are:Django 1.11 - Python 2.7 and 3.4 - 3.7,Django 2.0 - Python 3.4 - 3.7,Django 2.1 - Python 3.5 - 3.7,Django 2.2 - Python 3.5 - 3.7.UsageSet up a PartialIndex and insert it into your model's class-based Meta.indexes list:frompartial_indeximportPartialIndex,PQclassMyModel(models.Model):classMeta:indexes=[PartialIndex(fields=['user','room'],unique=True,where=PQ(deleted_at__isnull=True)),PartialIndex(fields=['created_at'],unique=False,where=PQ(is_complete=False)),]ThePQuses the exact same syntax and supports all the same features as Django'sQobjects (see Django docs for a full tutorial). It is provided for compatibility with Django 1.11.Of course, these (unique) indexes could be created by a handwrittenRunSQL migration.
But the constraints are part of the business logic, and best kept close to the model definitions.Partial unique constraintsWithunique=True, this can be used to create unique constraints for a subset of the rows.For example, you might have a model that has a deleted_at field to mark rows as archived instead of deleting them forever.
You wish to add unique constraints on "alive" rows, but allow multiple copies in the archive.Django's unique_togetheris not sufficient here, as that cannot
distinguish between the archived and alive rows.frompartial_indeximportPartialIndex,PQclassRoomBooking(models.Model):user=models.ForeignKey(User)room=models.ForeignKey(Room)deleted_at=models.DateTimeField(null=True,blank=True)classMeta:# unique_together = [('user', 'room')] - Does not allow multiple deleted rows. Instead use:indexes=[PartialIndex(fields=['user','room'],unique=True,where=PQ(deleted_at__isnull=True))]Partial non-unique indexesWithunique=False, partial indexes can be used to optimise lookups that return only a small subset of the rows.For example, you might have a job queue table which keeps an archive of millions of completed jobs. Among these are a few pending jobs,
which you want to find with a.filter(is_complete=0)query.frompartial_indeximportPartialIndex,PQclassJob(models.Model):created_at=models.DateTimeField(auto_now_add=True)is_complete=models.IntegerField(default=0)classMeta:indexes=[PartialIndex(fields=['created_at'],unique=False,where=PQ(is_complete=0))]Compared to an usual full index on theis_completefield, this can be significantly smaller in disk and memory use, and faster to update.Referencing multiple fields in the conditionWithF-expressions, you can create conditions that reference multiple fields:frompartial_indeximportPartialIndex,PQ,PFclassNotTheSameAgain(models.Model):a=models.IntegerField()b=models.IntegerField()classMeta:indexes=[PartialIndex(fields=['a','b'],unique=True,where=PQ(a=PF('b'))),]This PartialIndex allows multiple copies of(2, 3), but only a single copy of(2, 2)to exist in the database.ThePFuses the exact same syntax and supports all the same features as Django'sFexpressions (see Django docs for a full tutorial). It is provided for compatibility with Django 1.11.Unique validation on ModelFormsUnique partial indexes are validated by the PostgreSQL and SQLite databases. When they reject an INSERT or UPDATE, Django raises aIntegrityErrorexception. This results in a500 Server Errorstatus page in the browser if not handled before the database query is run.ModelForms perform unique validation before saving an object, and present the user with a descriptive error message.Adding an index does not modify the parent model's unique validation, so partial index validations are not handled by them by default. To add that to your model, include theValidatePartialUniqueMixinin your model definition:frompartial_indeximportPartialIndex,PQ,ValidatePartialUniqueMixinclassMyModel(ValidatePartialUniqueMixin,models.Model):classMeta:indexes=[PartialIndex(fields=['user','room'],unique=True,where=PQ(deleted_at__isnull=True)),]Note that it should be added on the model itself, not the ModelForm class.Adding the mixin for non-unique partial indexes is unnecessary, as they cannot cause database IntegrityErrors.Text-based where-conditions (deprecated)Text-based where-conditions are deprecated and will be removed in the next release (0.6.0) of django-partial-index.They are still supported in version 0.5.0 to simplify upgrading existing projects to thePQ-based indexes. New projects should not use them.frompartial_indeximportPartialIndexclassTextExample(models.Model):classMeta:indexes=[PartialIndex(fields=['user','room'],unique=True,where='deleted_at IS NULL'),PartialIndex(fields=['created_at'],unique=False,where_postgresql='is_complete = false',where_sqlite='is_complete = 0')]Version History0.6.0 (latest)Add support for Django 2.2.Document (already existing) support for Django 2.1 and Python 3.7.0.5.2Fix makemigrations for Django 1.11.Make sure PQ and PF are imported directly from partial_index in migration files.0.5.1Fix README formatting in PyPI.0.5.0Add support for Q-object based where-expressions.Deprecate support for text-based where-expressions. These will be removed in version 0.6.0.Add ValidatePartialUniqueMixin for model classes. This adds partial unique index validation for ModelForms, avoiding an IntegrityError and instead showing an error message as with usual unique_together constraints.0.4.0Add support for Django 2.0.0.3.0Add support for separatewhere_postgresql=''andwhere_sqlite=''predicates, when the expression has different syntax on the two
database backends and you wish to support both.0.2.1Ensure that automatically generated index names depend on the "unique" and "where" parameters. Otherwise two indexes with the same fields would be considered identical by Django.0.2.0Fully tested SQLite and PostgreSQL support.Tests for generated SQL statements, adding and removing indexes, and that unique constraints work when inserting rows into the db tables.Python 2.7, 3.4-3.6 support.0.1.1Experimental SQLite support.0.1.0First release, working but untested PostgreSQL support.Future plansAdd a validation mixin for DRF Serializers.Remove support for text-based where conditions.