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MongoDB and Python driver


Installing MongoDB

Installing MongoDB is pretty straight forward. Just download the right package from download page on mongo website, and then unarchive it somewhere. Create in that root directory a folder for data (mkdir -p data/db) and then fire up the server with: bin/mongod –dbpath data/db/.

Installing PyMongo

The python package is called PyMongo, and it's the right tool to work with MongoDB. An easy way to install it is to use easy_install tool.
Check this page to find out more information.

Creating/Connecting to a DB

Creating a db is very simple. First you get a connection to the running mongod and then simply point to the database name. This will be created lazily style (when you actually will insert something).

To get a connection for a different host or port, use Connection('different_host', 12345)

In [1]: from pymongo import Connection
In [2]: conn = Connection()
In [3]: db = conn.example_db
In [4]: db
Out[4]: Database(Connection('localhost', 27017), u'example_db')


The process is similar to the database creation one.

In [5]: collection = db.collection_example

Entering Data (Inserting documents)

Data in MongoDB is represented and stored using JSON-style documents. In PyMongo we use dictionaries to represent documents and to insert data the insert method is used.

In [6]: author_data = { "author" : "John Doe", "age": 54, "hobbies": [ "ski", "music", "writing poems" ]}
In [7]: collection.insert(author_data)
Out[7]: ObjectId('4bd5b83790dedd17d8000000')

When a document is inserted a special key, “_id”, is automatically added if the document doesn’t already contain an “_id” key. The value of “_id” must be unique across the collection. insert() returns the value of “_id” for the inserted document. For more information, see the documentation on _id.

To insert multiple documents, we pass an iterator to the insert() method like this:

In [16]: new_authors = [ { "author" : "Good Joe", "age": 22, "hobbies": [ "writing code", "music", "literature" ]},
                         { "author" : "Ryan Zoe", "age": 44, "hobbies": [  "chess", "literature" ]} ]
In [19]: collection.insert(new_authors)
Out[19]: [ObjectId('4bd5b9c890dedd17d8000001'), ObjectId('4bd5b9c890dedd17d8000002')]                

To get all the collections available in our database, use this:

In [8]: db.collection_names()
Out[8]: [u'collection_example', u'system.indexes']

Querying the collections

Methods: find_one and find.

In [23]: collection.find_one({"author": "John Doe"})
{u'_id': ObjectId('4bd5b83790dedd17d8000000'),
 u'age': 54,
 u'author': u'John Doe',
 u'hobbies': [u'ski', u'music', u'writing poems']}

In [32]: for author in collection.find():
   ....:     print "Author: %s Age: %s" % (author["author"], author["age"])
Author: John Doe Age: 54
Author: Good Joe Age: 22
Author: Ryan Zoe Age: 44

Using Regex in search function (don't forget to run first import re if it's not there already):

In [94]: collection.find({ "author": re.compile("John.*") }).count()
Out[94]: 1

collection.find({ "age" : { "$lt": 30 } }).count() # find all records with age less than 30

For advanced queries check

db/mongo_pythondriver.txt · Last modified: 2013/03/16 17:40 (external edit)