Support for PostgreSQL's hstore for Django.
Project description
Django-hstore is a niche library which integrates the hstore extension of PostgreSQL into Django, assuming one is using Django 1.2+, PostgreSQL 9.0+, and Psycopg 2.3+.
Limitations
Due to how Django implements its ORM, you will need to use the custom postgresql_psycopg2 backend defined in this package, which naturally will prevent you from dropping in other django extensions which require a custom backend (unless you fork and combine).
PostgreSQL’s implementation of hstore has no concept of type; it stores a mapping of string keys to string values. This library makes no attempt to coerce keys or values to strings.
Running the tests
Assuming one has the dependencies installed, and a PostgreSQL 9.0+ server up and running:
python setup.py test
Usage
First, update your settings module to specify the custom database backend:
DATABASES = { 'default': { 'ENGINE': 'django_hstore.postgresql_psycopg2', ... } }
Note to South users: If you keep getting errors like There is no South database module ‘south.db.None’ for your database., add the following to settings.py:
SOUTH_DATABASE_ADAPTERS = {'default': 'south.db.postgresql_psycopg2'}
The library provides three principal classes:
- django_hstore.hstore.DictionaryField
An ORM field which stores a mapping of string key/value pairs in an hstore column.
- django_hstore.hstore.ReferencesField
An ORM field which builds on DictionaryField to store a mapping of string keys to django object references, much like ForeignKey.
- django_hstore.hstore.HStoreManager
An ORM manager which provides much of the query functionality of the library.
Model definition is straightforward:
from django.db import models from django_hstore import hstore class Something(models.Model): name = models.CharField(max_length=32) data = hstore.DictionaryField() objects = hstore.HStoreManager() def __unicode__(self): return self.name
You then treat the data field as simply a dictionary of string pairs:
instance = Something.objects.create(name='something', data={'a': '1', 'b': '2'}) assert instance.data['a'] == '1' empty = Something.objects.create(name='empty') assert empty.data == {} empty.data['a'] = '1' empty.save() assert Something.objects.get(name='something').data['a'] == '1'
You can issue indexed queries against hstore fields:
# equivalence Something.objects.filter(data={'a': '1', 'b': '2'}) # subset by key/value mapping Something.objects.filter(data__contains={'a': '1'}) # subset by list of keys Something.objects.filter(data__contains=['a', 'b']) # subset by single key Something.objects.filter(data__contains='a')
You can also take advantage of some db-side functionality by using the manager:
# identify the keys present in an hstore field >>> Something.objects.hkeys(id=instance.id, attr='data') ['a', 'b'] # peek at a a named value within an hstore field >>> Something.objects.hpeek(id=instance.id, attr='data', key='a') '1' # do the same, after filter >>> Something.objects.filter(id=instance.id).hpeek(attr='data', key='a') '1' # remove a key/value pair from an hstore field >>> Something.objects.filter(name='something').hremove('data', 'b')
The hstore methods on manager pass all keyword arguments aside from attr and key to .filter().
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