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Description:

rom 1.1.1

Rom - the Redis object mapper for Python
Copyright 2013-2023 Josiah Carlson
Released under the LGPL license version 2.1 and version 3 (you can choose
which you’d like to be bound under).

Sponsorships Available
Don’t like LGPL? Sponsor the project and get almost any license you want.
This project has been partly sponsored by structd.com . Historically,
rom has been used to help support the delivery of millions of food orders for
chownow.com, and has been used as the primary backend and prototype for several
startups that have made it all the way to series A.
Thank you to our sponsors and those who have consumed our services.
You are welcome for the good service.
Your company link here.

Documentation
Updated documentation can be found: https://josiahcarlson.github.io/rom/

What
Rom is a package whose purpose is to offer active-record style data modeling
within Redis from Python, similar to the semantics of Django ORM, SQLAlchemy,
Google’s Appengine datastore, and others.

Why
I was building a personal project, wanted to use Redis to store some of my
data, but didn’t want to hack it poorly. I looked at the existing Redis object
mappers available in Python, but didn’t like the features and functionality
offered.

What is available
Data types:

Strings (2.x: str/unicode, 3.3+: str), ints, floats, decimals, booleans
datetime.datetime, datetime.date, datetime.time
Json columns (for nested structures)
OneToMany and ManyToOne columns (for model references)
Non-rom ForeignModel reference support

Indexes:

Numeric range fetches, searches, and ordering
Full-word text search (find me entries with col X having words A and B)
Prefix matching (can be used for prefix-based autocomplete)
Suffix matching (can be used for suffix-based autocomplete)
Pattern matching on string-based columns
All indexing except Geo indexing is available when using Redis 2.6.0 and
later
Geo indexing available with Redis 3.2.0 and later

Other features:

Per-thread entity cache (to minimize round-trips, easy saving of all
entities)
The ability to cache query results and get the key for any other use (see:
Query.cached_result())

Getting started

Make sure you have Python 2.6, 2.7, or 3.3+ installed
Make sure that you have Andy McCurdy’s Redis client library installed:
https://github.com/andymccurdy/redis-py/ or
https://pypi.python.org/pypi/redis
Make sure that you have the Python 2 and 3 compatibility library, ‘six’
installed: https://pypi.python.org/pypi/six
(optional) Make sure that you have the hiredis library installed for Python
Make sure that you have a Redis server installed and available remotely
Update the Redis connection settings for rom via
rom.util.set_connection_settings() (other connection update options,
including per-model connections, can be read about in the rom.util
documentation):
import redis
from rom import util

util.set_connection_settings(host='myhost', db=7)

Warning
If you forget to update the connection function, rom will attempt
to connect to localhost:6379 .

Create a model:
import rom

# All models to be handled by rom must derived from rom.Model
class User(rom.Model):
email = rom.String(required=True, unique=True, suffix=True)
salt = rom.String()
hash = rom.String()
created_at = rom.Float(default=time.time)

Create an instance of the model and save it:
PASSES = 32768
def gen_hash(password, salt=None):
salt = salt or os.urandom(16)
comp = salt + password
out = sha256(comp).digest()
for i in xrange(PASSES-1):
out = sha256(out + comp).digest()
return salt, out

user = User(email='user@host.com')
user.salt, user.hash = gen_hash(password)
user.save()
# session.commit() or session.flush() works too

Load and use the object later:
user = User.get_by(email='user@host.com')
at_gmail = User.query.endswith(email='@gmail.com').all()

Lua support
From version 0.25.0 and on, rom assumes that you are using Redis version 2.6
or later, which supports server-side Lua scripting. This allows for the
support of multiple unique column constraints without annoying race conditions
and retries. This also allows for the support of prefix, suffix, and pattern
matching on certain column types.
If you are using a version of Redis prior to 2.6, you should upgrade Redis. If
you are unable or unwilling to upgrade Redis, but you still wish to use rom,
you should call rom._disable_lua_writes(), which will prevent you from
using features that require Lua scripting support.

Expiring models/TTLs
There is a series of feature requests/bug reports/pull requests to add the
ability for rom to automatically delete and/or expire entity data stored in
Redis. This is a request that has been made (as of January 2016) 6 different
times.
Long story short: rom stores a bunch of data in secondary structures to make
querying fast. When a model “expires”, that data doesn’t get deleted. To
delete that data, you have to run a cleanup function that literally has to
scan over every entity in order to determine if the model had been expired. That
is a huge waste and is the antithesis of good design.
Instead, if you create a new expire_at float column with index=True,
the column can store when the entity is to expire. Then to expire the data, you
can use: Model.query.filter(expire_at=(0, time.time())).limit(10) to (for
example) get up to the 10 oldest entities that need to be expired.
Now, I know what you are thinking. You are thinking, “but I wish the data would
just go away on its own.” And I don’t disagree. But for that to happen, Redis
needs to grow Lua-script triggers, or you need to run a separate daemon to
periodically clean up left-over data. But … if you need to run a separate
daemon to clean up left-over data by scanning all of your rom entities,
wouldn’t it just be better/faster in every way to keep an explicit column and do
it efficiently? I think so, and you should too.