djorm-ext-hstore 0.4.2

================
djorm-ext-hstore
================

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

Compatible with django: 1.4 and posible with 1.3. Django 1.5 and python3.2+ compatibility coming soon.

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.


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:

.. code-block:: python

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:

.. code-block:: python

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:


.. code-block:: python

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:

.. code-block:: python

# 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.

.. code-block:: python

from djorm_hstore.functions import HstoreSlice, HstorePeek, HstoreKeys

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