Using
MongoDB
as your primary
Django database

By Andre Medeiros at DjangoCon Finland 2013

Who?

Andre Medeiros

Founder at Iroquote.com
Next generation discussion forums

@andrestaltz

Brazilian that doesn't play soccer

M.Sc. from Aalto University

MongoDB is
Agile and Scalable

• Dynamic schemas
• Index on any attribute
• Auto-sharding

→ Popular NoSQL database

Why MongoDB for Django?

The “pythonic database”

# Python
person = {
	'name': "John Doe", 
	'skills': ["Javascript", "CSS", "HTML"],
	'work': None
}
						

// Javascript
person = {
	"name" : "John Doe", 
	"skills" : ["Javascript", "CSS", "HTML"],
	"work" : null
};
						

Writing Python is fun, and keeping everything in Python limits the number of times your brain has to do a "context switch." It helps productivity if you keep yourself in a single programming environment/mentality for as long as possible.

If MongoDB had existed 10 years ago the vast majority of data used to drive modern web applications would be stored in MongoDB and not a relational database.

Real world example

{
	"_id" : ObjectId("5500165de50c050005e4b29f"),
	"title" : "Using MongoDB as your primary Django database",
	"message" : "This presentation introduces MongoDB to Django de...",
	"author" : ObjectId("5182953ba50c051575e4b29c"),
	"creation_date" : ISODate("2013-05-21T12:44:31.408Z"),
	"tags" : ["django","python","mongodb","mongoengine","nosql"],
	"comments" : [
		{
			"author" :  ObjectId("50c90b3128650a004200961a"),
			"message" : "Nice, I didn't know this was possible."
		}
	],
}
						

with MongoDB

At the core of Django is its ORM

MongoEngine
is an Object-Document Mapper made for MongoDB, following Django's ORM style.

pip install mongoengine==0.8.0
					

MongoEngine model

from mongoengine import *

class Choice(EmbeddedDocument):
    choice_text = StringField(max_length=200)
    votes = IntField(default=0)

class Poll(Document):
    question = StringField(max_length=200)
    pub_date = DateTimeField(help_text='date published')
    choices = ListField(EmbeddedDocumentField(Choice))
					

Translated to MongoDB...

{
	"_id" : ObjectId("5483165de50c050005e4b29f"),
	"question" : "What's up?",
	"pub_date" :  ISODate("2013-04-14T11:06:21.922Z"),
	"choices" : [
		{
			"choice_text" : "Not much",
			"votes" : 0
		},
		{
			"choice_text" : "Just hacking again",
			"votes" : 1
		}
	],
}
					

Querying and updating

from yourproject.models import Poll, Choice

poll = Poll.objects(question__contains="What").first()
choice = Choice(choice_text="I'm at DjangoCon.fi", votes=23)
poll.choices.append(choice)
poll.save()

print poll.question
					

Setting indexes

class Poll(Document):
	question = StringField(max_length=200)
	pub_date = DateTimeField(help_text='date published')
	choices = ListField(EmbeddedDocumentField(Choice))

	meta = {
		'indexes': [
			'question', 
			('pub_date', '+question')
		]
	}
					

The fun side

The painful side

Django, forget your databases

import mongoengine

DATABASES = {
	'default': {
		'ENGINE': '',
	},
}

SESSION_ENGINE = 'mongoengine.django.sessions' # optional
					

Connect to MongoDB

_MONGODB_USER = 'mongouser'
_MONGODB_PASSWD = 'password'
_MONGODB_HOST = 'thehost'
_MONGODB_NAME = 'thedb'
_MONGODB_DATABASE_HOST = \
	'mongodb://%s:%s@%s/%s' \
	% (_MONGODB_USER, _MONGODB_PASSWD, _MONGODB_HOST, _MONGODB_NAME)

mongoengine.connect(_MONGODB_NAME, host=_MONGODB_DATABASE_HOST)
					

Use MongoEngine's User

AUTHENTICATION_BACKENDS = (
	'mongoengine.django.auth.MongoEngineBackend',
)
					

import mongoengine

# ...

user = authenticate(username=username, password=password)
assert isinstance(user, mongoengine.django.auth.User)
					

Hack the test runner

from django.test.simple import DjangoTestSuiteRunner
from django.test import TestCase

class NoSQLTestRunner(DjangoTestSuiteRunner):
	def setup_databases(self):
		pass
	def teardown_databases(self, *args):
		pass

class NoSQLTestCase(TestCase):
	def _fixture_setup(self):
		pass
	def _fixture_teardown(self):
		pass
						

TEST_RUNNER = 'yourproject.tests.NoSQLTestRunner'
						

Or use Mongorunner

MongoEngine is good

• Maintained and updated constantly by 10gen
• Solid and works like Django's ORM
• A replaceable component in Django

Alternative to MongoEngine

When NOT to use MongoDB

• You need ACID transactions
• You have a stable SQL database in production
• You need the most stable RDBMS you can get

Consider MongoDB when...

• You are starting a project with design freedom
• Your app has an evolving data schema
• Your want auto-sharding on a simple schema
• Your app has plenty of geospatial data
• You have high-volume traffic
• Your app works around a RESTful JSON API

Thank you