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djorm-ext-hstore

Is the library which integrates the hstore extension of PostgreSQL into Django,

Compatible with django >= 1.4

Limitations and notes

  • 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.
  • Hstore extension is not automatically installed on use this package. You must install it manually. (For execute tests, you must install hstore extension on template1 database.

Classes

The library provides three principal classes:

djorm_hstore.fields.DictionaryField
An ORM field which stores a mapping of string key/value pairs in an hstore column.
djorm_hstore.fields.ReferencesField
An ORM field which builds on DictionaryField to store a mapping of string keys to django object references, much like ForeignKey.
djorm_hstor.models.HStoreManager
An ORM manager which provides much of the query functionality of the library.

NOTE: the predefined hstore manager inherits all functionality of djorm-ext-expressions module (which is part of django orm extensions package)

Usage

Initially define some sample model:

from django.db import models
from djorm_hstore.fields import DictionaryField
from djorm_hstore.models import HStoreManager

class Something(models.Model):
    name = models.CharField(max_length=32)
    data = DictionaryField(db_index=True)
    objects = 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:

from djorm_hstore.expressions import HstoreExpression as HE

# equivalence
Something.objects.filter(data={'a': '1', 'b': '2'})

# subset by key/value mapping
Something.objects.where(HE("data").contains({'a':'1'}))

# subset by list of keys
Something.objects.where(HE("data").contains(['a', 'b']))

# subset by single key
Something.objects.where(HE("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.filter(id=1).hkeys(attr='data')
['a', 'b']

# peek at a a named value within an hstore field
>>> Something.objects.filter(id=1).hpeek(attr='data', key='a')
'1'

# remove a key/value pair from an hstore field
>>> Something.objects.filter(name='something').hremove('data', 'b')

In addition to filters and specific methods to retrieve keys or hstore field values, we can also use annotations, and then we can filter for them.

from djorm_hstore.functions import HstoreSlice, HstorePeek, HstoreKeys

queryset = SomeModel.objects.annotate_functions(
    sliced = HstoreSlice("hstorefield", ['v']),
    peeked = HstorePeek("hstorefield", "v"),
    keys = HstoreKeys("hstorefield"),
)