This document summarizes MongoEngine, an ORM (object-relational mapper) for working with MongoDB in Python. It introduces MongoDB as a scalable, high-performance, document-oriented NoSQL database. It compares MongoDB to RDBMS and shows how MongoEngine allows defining schemas and querying/updating data similarly to an ORM for SQL, while still maintaining flexibility of MongoDB. It provides examples of defining schemas using MongoEngine classes, querying data, updating documents, and how MongoEngine interacts with PyMongo and MongoDB under the hood. It also briefly discusses performance and integration with Django.

1. MongoEngine
NoORM for NoSQL
Serge Matveenko
github.com/lig
PyCon Russia 2013

2. Quick MongoDB intro
NoSQL document-oriented database
● scalable (auto-sharding, replication)
● high-performance (~104-105 queries/sec)
● open source (db: AGPL, drivers: Apache)

3. RDBMS vs MongoDB
RDBMS MongoDB
data DB + Driver DB + PyMongo
aggregation
constraints Application
validation
cascade updates
business logic Application

4. RDBMS vs MongoDB
RDBMS MongoDB
data DB + Driver DB + PyMongo
aggregation
constraints MongoEngine
validation
cascade updates
business logic Application Application

5. How it looks
MongoEngine class CharacterName(EmbeddedDocument):
first = StringField()
last = StringField()
class Character(Document):
name = EmbeddedDocumentField(CharacterName)
rating = IntField()
MongoDB {
"_id" : ObjectId
("5125e0ee98764119e77d9b1f"),
"_types" : ["Character"],
"rating" : 42,
"name" : {"_types" : ["CharacterName"],
"last": "Connor", "_cls": "CharacterName",
"first": "Sarah"},
"_cls": "Character"
}

6. How it looks
(MongoEngine 0.8)
MongoEngine class CharacterName(EmbeddedDocument):
first = StringField()
last = StringField()
class Character(Document):
name = EmbeddedDocumentField(CharacterName)
rating = IntField()
MongoDB {
"_id" : ObjectId
("5125e0ee98764119e77d9b1f"),
"rating" : 42,
"name" : {"last": "Connor",
"_cls": "CharacterName", "first": "Sarah"},
"_cls": "Character"
}

7. Querying with MongoEngine
Simple
db.character.find({'name.first': 'John'})
Character.objects(name__first='John')
db.character.find({rating: {$gte: 42}}).limit(5)
Character.objects(rating__gte=42)[:5]
db.character.find({rating: {$exists: false}})
Character.objects(rating__exists=False)

8. Querying with MongoEngine
Map/Reduce
db.character.mapReduce(map_f, reduce_f, {out: 'mr_col'});
db.mr_col.find();
Character.objects.map_reduce(map_f, reduce_f, 'mr_col')

9. Updating with MongoEngine
Creating
db.character.save(
{name: {first: 'John', last: 'Conor'}, rating: 42})
jc = Character(
name=CharacterName(first='John', last='Conor'),
rating=42)
jc.save()

10. Updating with MongoEngine
Atomic updates
db.character.update(
{name: {first: "John", last: "Conor"}},
{$set: {"name.last": "Connor"}})
Character.objects(
name=CharacterName(first='John', last='Conor')
).update(set__name__last='Connor')

11. Under the hood
"C" BSON
MongoDB PyMongo MongoEngine
Module
s es
pe ass
data tiv e ty e cl
Bina
ry na ativ
yt hon De clar
P
JavaScript
Console

12. Under the hood
"C" BSON
MongoDB PyMongo MongoEngine
Module
s es
pe ass
data tiv e ty e cl
Bina
ry na ativ
yt hon De clar
P
JavaScript
Console

13. Performance

14. Django integration
Out of the box
● authentication backend
● session engine
● GridFSStorage
Third party
● stephrdev/django-mongoforms (Model Forms port)
● wpjunior/django-mongotools (forms, generic views)
● lig/django-registration-me (django-registration port)

15. Customizing things
(added today. sorry:)
● SequenceField(value_decorator=func)
● StringField(regex=r'…')
● URLField(verify_exists=True)
● …
● Inherit from standard Field classes
● Write your own Field classes
● Inherit from BaseDocument class,
don't forget metaclass!
● Any metamagic your like…

16. Questions?
Serge Matveenko (github.com/lig)
mongoengine.org
www.mongodb.org
Thanks to
Ross Lawley (github.com/rozza)
Elena Voronina :)