Flask-PyMongo

MongoDB is an open source database that stores flexible JSON-like “documents,” which can have any number, name, or hierarchy of fields within, instead of rows of data as in a relational database. Python developers can think of MongoDB as a persistent, searchable repository of Python dictionaries (and, in fact, this is how PyMongo represents MongoDB documents).

Flask-PyMongo bridges Flask and PyMongo, so that you can use Flask’s normal mechanisms to configure and connect to MongoDB.

Quickstart

First, install Flask-PyMongo:

$ pip install Flask-PyMongo

Flask-PyMongo depends, and will install for you, recent versions of Flask (0.8 or later) and PyMongo (2.4 or later). Flask-PyMongo is compatible with and tested on Python 2.6, 2.7, and 3.3.

Next, add a PyMongo to your code:

from flask import Flask
from flask.ext.pymongo import PyMongo

app = Flask(__name__)
mongo = PyMongo(app)

PyMongo connects to the MongoDB server running on port 27017 on localhost, and assumes a default database name of app.name (i.e. whatever name you pass to Flask). This database is exposed as the db attribute.

You can use db directly in views:

@app.route('/')
def home_page():
    online_users = mongo.db.users.find({'online': True})
    return render_template('index.html',
        online_users=online_users)

Helpers

Flask-PyMongo provides helpers for some common tasks:

Collection.find_one_or_404(*args, **kwargs)

Find and return a single document, or raise a 404 Not Found exception if no document matches the query spec. See find_one() for details.

@app.route('/user/<username>')
def user_profile(username):
    user = mongo.db.users.find_one_or_404({'_id': username})
    return render_template('user.html',
        user=user)
PyMongo.send_file(filename, base='fs', version=-1, cache_for=31536000)

Return an instance of the response_class containing the named file, and implement conditional GET semantics (using make_conditional()).

@app.route('/uploads/<path:filename>')
def get_upload(filename):
    return mongo.send_file(filename)
Parameters:
  • filename (str) – the filename of the file to return
  • base (str) – the base name of the GridFS collections to use
  • version (bool) – if positive, return the Nth revision of the file identified by filename; if negative, return the Nth most recent revision. If no such version exists, return with HTTP status 404.
  • cache_for (int) – number of seconds that browsers should be instructed to cache responses
PyMongo.save_file(filename, fileobj, base='fs', content_type=None)

Save the file-like object to GridFS using the given filename. Returns None.

@app.route('/uploads/<path:filename>', methods=['POST'])
def save_upload(filename):
    mongo.save_file(filename, request.files['file'])
    return redirect(url_for('get_upload', filename=filename))
Parameters:
  • filename (str) – the filename of the file to return
  • fileobj (file) – the file-like object to save
  • base (str) – base the base name of the GridFS collections to use
  • content_type (str) – the MIME content-type of the file. If None, the content-type is guessed from the filename using guess_type()
class flask_pymongo.BSONObjectIdConverter(map)

A simple converter for the RESTful URL routing system of Flask.

@app.route('/<ObjectId:task_id>')
def show_task(task_id):
    task = mongo.db.tasks.find_one_or_404(task_id)
    return render_template('task.html', task=task)

Valid object ID strings are converted into ObjectId objects; invalid strings result in a 404 error. The converter is automatically registered by the initialization of PyMongo with keyword ObjectId.

Configuration

PyMongo understands the following configuration directives:

MONGO_URI A MongoDB URI which is used in preference of the other configuration variables.
MONGO_HOST The host name or IP address of your MongoDB server. Default: “localhost”.
MONGO_PORT The port number of your MongoDB server. Default: 27017.
MONGO_AUTO_START_REQUEST Set to False to disable PyMongo 2.2’s “auto start request” behavior (see MongoClient). Default: True.
MONGO_MAX_POOL_SIZE (optional): The maximum number of idle connections maintained in the PyMongo connection pool. Default: PyMongo default.
MONGO_SOCKET_TIMEOUT_MS (optional): (integer) How long (in milliseconds) a send or receive on a socket can take before timing out. Default: PyMongo default.
MONGO_CONNECT_TIMEOUT_MS (optional): (integer) How long (in milliseconds) a connection can take to be opened before timing out. Default: PyMongo default.
MONGO_DBNAME The database name to make available as the db attribute. Default: app.name.
MONGO_USERNAME The user name for authentication. Default: None
MONGO_PASSWORD The password for authentication. Default: None
MONGO_REPLICA_SET The name of a replica set to connect to; this must match the internal name of the replica set (as deteremined by the isMaster command). Default: None.
MONGO_READ_PREFERENCE Determines how read queries are routed to the replica set members. Must be one of the constants defined on pymongo.read_preferences.ReadPreference or the string names thereof
MONGO_DOCUMENT_CLASS This tells pymongo to return custom objects instead of dicts, for example bson.son.SON. Default: dict
MONGO_CONNECT (optional): If True (the default), let the MongoClient immediately begin connecting to MongoDB in the background. Otherwise connect on the first operation. This has to be set to False if multiprocessing is desired; see Using PyMongo with Multiprocessing.

When PyMongo or init_app() are invoked with only one argument (the Flask instance), a configuration value prefix of MONGO is assumed; this can be overridden with the config_prefix argument.

This technique can be used to connect to multiple databases or database servers:

app = Flask(__name__)

# connect to MongoDB with the defaults
mongo1 = PyMongo(app)

# connect to another MongoDB database on the same host
app.config['MONGO2_DBNAME'] = 'dbname_two'
mongo2 = PyMongo(app, config_prefix='MONGO2')

# connect to another MongoDB server altogether
app.config['MONGO3_HOST'] = 'another.host.example.com'
app.config['MONGO3_PORT'] = 27017
app.config['MONGO3_DBNAME'] = 'dbname_three'
mongo3 = PyMongo(app, config_prefix='MONGO3')

Some auto-configured settings that you should be aware of are:

tz_aware:
Flask-PyMongo always uses timezone-aware datetime objects. That is, it sets the tz_aware parameter to True when creating a connection. The timezone of datetime objects returned from MongoDB will always be UTC.
safe:
Flask-PyMongo sets “safe” mode by default, which causes save(), insert(), update(), and remove() to wait for acknowledgement from the server before returning. You may override this on a per-call basis by passing the keyword argument safe=False to any of the effected methods.

API

Constants

flask_pymongo.ASCENDING = 1

Ascending sort order.

flask_pymongo.DESCENDING = -1

Descending sort order.

Classes

class flask_pymongo.PyMongo(app=None, config_prefix='MONGO')

Automatically connects to MongoDB using parameters defined in Flask configuration.

cx

The automatically created Connection or ReplicaSetConnection object.

db

The automatically created Database object corresponding to the provided MONGO_DBNAME configuration parameter.

init_app(app, config_prefix='MONGO')

Initialize the app for use with this PyMongo. This is called automatically if app is passed to __init__().

The app is configured according to the configuration variables PREFIX_HOST, PREFIX_PORT, PREFIX_DBNAME, PREFIX_AUTO_START_REQUEST, PREFIX_REPLICA_SET, PREFIX_READ_PREFERENCE, PREFIX_USERNAME, PREFIX_PASSWORD, and PREFIX_URI where “PREFIX” defaults to “MONGO”. If PREFIX_URL is set, it is assumed to have all appropriate configurations, and the other keys are overwritten using their values as present in the URI.

Parameters:
  • app (flask.Flask) – the application to configure for use with this PyMongo
  • config_prefix (str) – determines the set of configuration variables used to configure this PyMongo
save_file(filename, fileobj, base='fs', content_type=None)

Save the file-like object to GridFS using the given filename. Returns None.

@app.route('/uploads/<path:filename>', methods=['POST'])
def save_upload(filename):
    mongo.save_file(filename, request.files['file'])
    return redirect(url_for('get_upload', filename=filename))
Parameters:
  • filename (str) – the filename of the file to return
  • fileobj (file) – the file-like object to save
  • base (str) – base the base name of the GridFS collections to use
  • content_type (str) – the MIME content-type of the file. If None, the content-type is guessed from the filename using guess_type()
send_file(filename, base='fs', version=-1, cache_for=31536000)

Return an instance of the response_class containing the named file, and implement conditional GET semantics (using make_conditional()).

@app.route('/uploads/<path:filename>')
def get_upload(filename):
    return mongo.send_file(filename)
Parameters:
  • filename (str) – the filename of the file to return
  • base (str) – the base name of the GridFS collections to use
  • version (bool) – if positive, return the Nth revision of the file identified by filename; if negative, return the Nth most recent revision. If no such version exists, return with HTTP status 404.
  • cache_for (int) – number of seconds that browsers should be instructed to cache responses
class flask_pymongo.wrappers.Collection(database, name, create=False, codec_options=None, read_preference=None, write_concern=None, read_concern=None, **kwargs)

Custom sub-class of pymongo.collection.Collection which adds Flask-specific helper methods.

find_one_or_404(*args, **kwargs)

Find and return a single document, or raise a 404 Not Found exception if no document matches the query spec. See find_one() for details.

@app.route('/user/<username>')
def user_profile(username):
    user = mongo.db.users.find_one_or_404({'_id': username})
    return render_template('user.html',
        user=user)

Wrappers

These classes exist solely in order to make expressions such as mongo.db.foo.bar evaluate to a Collection instance instead of a pymongo.collection.Collection instance. They are documented here solely for completeness.

class flask_pymongo.wrappers.MongoClient(host=None, port=None, document_class=<type 'dict'>, tz_aware=False, connect=True, **kwargs)

Returns instances of flask_pymongo.wrappers.Database instead of pymongo.database.Database when accessed with dot notation.

class flask_pymongo.wrappers.MongoReplicaSetClient(*args, **kwargs)

Returns instances of flask_pymongo.wrappers.Database instead of pymongo.database.Database when accessed with dot notation.

class flask_pymongo.wrappers.Database(client, name, codec_options=None, read_preference=None, write_concern=None, read_concern=None)

Returns instances of flask_pymongo.wrappers.Collection instead of pymongo.collection.Collection when accessed with dot notation.

History and Contributors

Changes: - 0.4.1: January 25, 2016

  • Add the connect keyword: #67.
  • 0.4.0: October 19, 2015
    • Flask-Pymongo is now compatible with pymongo 3.0+: #63.
  • 0.3.1: April 9, 2015
    • Flask-PyMongo is now tested against Python 2.6, 2.7, 3.3, and 3.4.
    • Flask-PyMongo installation now no longer depends on nose.
    • #58 Update requirements for PyMongo 3.x (Emmanuel Valette).
    • #43 Ensure error is raised when URI database name is parsed as ‘None’ (Ben Jeffrey).
    • #50 Fix a bug in read preference handling (Kevin Funk).
    • #46 Cannot use multiple replicaset instances which run on different ports (Mark Unsworth).
    • #30 ConfiguationError with MONGO_READ_PREFERENCE (Mark Unsworth).
  • 0.3.0: July 4, 2013
    • This is a minor version bump which introduces backwards breaking changes! Please read these change notes carefully.
    • Removed read preference constants from Flask-PyMongo; to set a read preference, use the string name or import contants directly from pymongo.read_preferences.ReadPreference.
    • #22 (partial) Add support for MONGO_SOCKET_TIMEOUT_MS and MONGO_CONNECT_TIMEOUT_MS options (ultrabug).
    • #27 (partial) Make Flask-PyMongo compatible with Python 3 (Vizzy).
  • 0.2.1: December 22, 2012
    • #19 Added MONGO_DOCUMENT_CLASS config option (jeverling).
  • 0.2.0: December 15, 2012
    • This is a minor version bump which may introduce backwards breaking changes! Please read these change notes carefully.
    • #17 Now using PyMongo 2.4’s MongoClient and MongoReplicaSetClient objects instead of Connection and ReplicaSetConnection classes (tang0th).
    • #17 Now requiring at least PyMongo version 2.4 (tang0th).
    • #17 The wrapper class flask_pymongo.wrappers.Connection is renamed to flask_pymongo.wrappers.MongoClient (tang0th).
    • #17 The wrapper class flask_pymongo.wrappers.ReplicaSetConnection is renamed to flask_pymongo.wrappers.MongoReplicaSetClient (tang0th).
    • #18 MONGO_AUTO_START_REQUEST now defaults to False when connecting using a URI.
  • 0.1.4: December 15, 2012
    • #15 Added support for MONGO_MAX_POOL_SIZE (Fabrice Aneche)
  • 0.1.3: September 22, 2012
    • Added support for configuration from MongoDB URI.
  • 0.1.2: June 18, 2012
    • Updated wiki example application
    • #14 Added examples and docs to PyPI package.
  • 0.1.1: May 26, 2012
    • Added support for PyMongo 2.2’s “auto start request” feature, by way of the MONGO_AUTO_START_REQUEST configuration flag.
    • #13 Added BSONObjectIdConverter (Christoph Herr)
    • #12 Corrected documentation typo (Thor Adam)
  • 0.1: December 21, 2011
    • Initial Release

Contributors: