Redisco

Python Containers and Simple Models for Redis

Description

Redisco allows you to store objects in Redis. It is inspired by the Ruby library Ohm and its design and code are loosely based on Ohm and the Django ORM. It is built on top of redis-py. It includes container classes that allow easier access to Redis sets, lists, and sorted sets.

Installation

Redisco requires redis-py 2.0.0 so get it first.

pip install redis

Then install redisco.

pip install redisco

Models

from redisco import models
class Person(models.Model):
    name = models.Attribute(required=True)
    created_at = models.DateTimeField(auto_now_add=True)
    fave_colors = models.ListField(str)

>>> person = Person(name="Conchita")
>>> person.is_valid()
True
>>> person.save()
True
>>> conchita = Person.objects.filter(name='Conchita')[0]
>>> conchita.name
'Conchita'
>>> conchita.created_at
datetime.datetime(2010, 5, 24, 16, 0, 31, 954704)

Model Attributes

Attribute

Stores unicode strings. If used for large bodies of text, turn indexing of this field off by setting indexed=True.

IntegerField

Stores an int. Ints are stringified using unicode() before saving to Redis.

Counter

An IntegerField that can only be accessed via Model.incr and Model.decr.

DateTimeField

Can store a DateTime object. Saved in the Redis store as a float.

DateField

Can store a Date object. Saved in Redis as a float.

FloatField

Can store floats.

BooleanField

Can store bools. Saved in Redis as 1's and 0's.

ReferenceField

Can reference other redisco model.

ListField

Can store a list of unicode, int, float, as well as other redisco models.

Attribute Options

required

If True, the attirbute cannot be None or empty. Strings are stripped to check if they are empty. Default is False.

default

Sets the default value of the attribute. Default is None.

indexed

If True, redisco will create index entries for the attribute. Indexes are used in filtering and ordering results of queries. For large bodies of strings, this should be set to False. Default is True.

validator

Set this to a callable that accepts two arguments -- the field name and the value of the attribute. The callable should return a list of tuples with the first item is the field name, and the second item is the error.

unique

The field must be unique. Default is False.

DateField and DateTimeField Options

auto_now_add

Automatically set the datetime/date field to now/today when the object is first created. Default is False.

auto_now

Automatically set the datetime/date field to now/today everytime the object is saved. Default is False.

Saving and Validating

To save an object, call its save method. This returns True on success (i.e. when the object is valid) and False otherwise.

Calling Model.is_valid will validate the attributes and lists. Model.is_valid is called when the instance is being saved. When there are invalid fields, Model.errors will hold the list of tuples containing the invalid fields and the reason for its invalidity. E.g. [('name', 'required'),('name', 'too short')]

Fields can be validated using the validator argument of the attribute. Just pass a callable that accepts two arguments -- the field name and the value of the attribute. The callable should return a list of errors.

Model.validate will also be called before saving the instance. Override it to validate instances not related to attributes.

def not_me(field_name, value):
    if value == 'Me':
        return ((field_name, 'it is me'),)

class Person(models.Model):
    name = models.Attribute(required=True, validator=not_me)
    age = models.IntegerField()

    def validate(self):
        if self.age and self.age < 21:
            self._errors.append(('age', 'below 21'))

>>> person = Person(name='Me')
>>> person.is_valid()
False
>>> person.errors
[('name', 'it is me')]

Queries

Queries are executed using a manager, accessed via the objects class attribute.

Person.objects.all()
Person.objects.filter(name='Conchita')
Person.objects.filter(name='Conchita').first()
Person.objects.all().order('name')
Person.objects.filter(fave_colors='Red')

Ranged Queries

Redisco has a limited support for queries involving ranges -- it can only filter fields that are numeric, i.e. DateField, DateTimeField, IntegerField, and FloatField. The zfilter method of the manager is used for these queries.

Person.objects.zfilter(created_at__lt=datetime(2010, 4, 20, 5, 2, 0))
Person.objects.zfilter(created_at__gte=datetime(2010, 4, 20, 5, 2, 0))
Person.objects.zfilter(created_at__in=(datetime(2010, 4, 20, 5, 2, 0), datetime(2010, 5, 1)))

Containers

Redisco has three containers that roughly match Redis's supported data structures: lists, sets, sorted set. Anything done to the container is persisted to Redis.

Sets

>>> from redisco.containers import Set
>>> s = Set('myset')
>>> s.add('apple')
>>> s.add('orange')
>>> s.members
set(['orange', 'apple'])
>>> t = Set('nset')
>>> t.add('kiwi')
>>> t.add('guava')
>>> t.members
set(['kiwi', 'guava'])
>>> s.update(t)
>>> s.members
set(['kiwi', 'orange', 'guava', 'apple'])

Lists

>>> import redis
>>> from redisco.containers import List
>>> l = List('alpha')
>>> l.append('a')
>>> l.append('b')
>>> l.append('c')
>>> 'a' in l
True
>>> 'd' in l
False
>>> len(l)
3
>>> l.index('b')
1
>>> l.members
['a', 'b', 'c']

Sorted Sets

>>> zset = SortedSet('zset')
>>> zset.members
['d', 'a', 'b', 'c']
>>> 'e' in zset
False
>>> 'a' in zset
True
>>> zset.rank('d')
0
>>> zset.rank('b')
2
>>> zset[1]
'a'
>>> zset.add('f', 200)
>>> zset.members
['d', 'a', 'b', 'c', 'f']
>>> zset.add('d', 99)
>>> zset.members
['a', 'b', 'c', 'd', 'f']

Dicts/Hashes

>>> h = cont.Hash('hkey')
>>> len(h)
0
>>> h['name'] = "Richard Cypher"
>>> h['real_name'] = "Richard Rahl"
>>> h
<Hash 'hkey' {'name': 'Richard Cypher', 'real_name': 'Richard Rahl'}>
>>> h.dict
{'name': 'Richard Cypher', 'real_name': 'Richard Rahl'}

Additional Info on Containers

Some methods of the Redis client that require the key as the first argument can be accessed from the container itself.

>>> l = List('mylist')
>>> l.lrange(0, -1)
0
>>> l.rpush('b')
>>> l.rpush('c')
>>> l.lpush('a')
>>> l.lrange(0, -1)
['a', 'b', 'c']
>>> h = Hash('hkey')
>>> h.hset('name', 'Richard Rahl')
>>> h
<Hash 'hkey' {'name': 'Richard Rahl'}>

Connecting to Redis

All models and containers use a global Redis client object to interact with the key-value storage. By default, it connects to localhost:6379, selecting db 0. If you wish to specify settings:

import redisco
redisco.connection_setup(host='localhost', port=6380, db=10)

The arguments to connect are simply passed to the redis.Redis init method.

For the containers, you can specify a second argument as the Redis client. That client object will be used instead of the default.

>>> import redis
>>> r = redis.Redis(host='localhost', port=6381)
>>> Set('someset', r)

Credits

Most of the concepts are taken from Soveran's Redis related Ruby libraries. cyx for sharing his expertise in indexing in Redis. Django, of course, for the popular model API.