Build Status


This API documentation is available online at for all releases of the MongoDB Ruby driver. Please reference the exact version of the documentation that matches the release of the Ruby driver that you are using. Note that the Ruby Language Center for MongoDB has a link to API Documentation for the current release.

If you have the source, you can generate the matching documentation by typing

sh $ rake docs

Once generated, the API documentation can be found in the docs/ folder.


This is the 10gen-supported Ruby driver for MongoDB.

For the api reference please see the API

The wiki has other articles of interest, including:

  1. A tutorial.
  2. Replica Sets in Ruby.
  3. Write Concern in Ruby.
  4. Tailable Cursors in Ruby.
  5. Read Preference in Ruby.
  6. GridFS in Ruby.
  7. Frequently Asked Questions.
  8. History.
  9. Release plan.
  10. Credits.

Here’s a quick code sample. Again, see the MongoDB Ruby Tutorial for much more:

```ruby require ‘rubygems’ require ‘mongo’

include Mongo

@client =‘localhost’, 27017) @db = @client[‘sample-db’] @coll = @db[‘test’]


3.times do |i| @coll.insert(=> i+1) end

puts “There are #@coll@coll.count records. Here they are:” @coll.find.each { |doc| puts doc.inspect } ```


Ruby Versions

The driver works and is consistently tested on Ruby 1.8.7 and 1.9.3 as well as JRuby 1.6.x and 1.7.x.

Note that if you’re on 1.8.7, be sure that you’re using a patchlevel >= 249. There are some IO bugs in earlier versions.


sh $ gem update --system $ gem install mongo

For a significant performance boost, you’ll want to install the C extension:

sh $ gem install bson_ext

Note that bson_ext isn’t used with JRuby. Instead, we use some native Java extensions are bundled with the bson gem. If you ever need to modify these extensions, you can recompile with the following rake task:

sh $ rake compile:jbson

From the GitHub source

The source code is available at You can either clone the git repository or download a tarball or zip file. Once you have the source, you can use it from wherever you downloaded it or you can install it as a gem from the source by typing:

sh $ rake install


For extensive examples, see the MongoDB Ruby Tutorial.


The Ruby driver include two abstractions for storing large files: Grid and GridFileSystem.

The Grid class is a Ruby implementation of MongoDB’s GridFS file storage specification. GridFileSystem is essentially the same, but provides a more filesystem-like API and assumes that filenames are unique.

An instance of both classes represents an individual file store. See the API reference for details.


```ruby # Write a file on disk to the Grid file =‘image.jpg’) grid = id = grid.put(file)

Retrieve the file

file = grid.get(id)

Get all the file’s metata

file.filename file.content_type file.metadata ```


Thread Safety

The driver is thread-safe.

Connection Pooling

The driver implements connection pooling. By default, only one socket connection will be opened to MongoDB. However, if you’re running a multi-threaded application, you can specify a maximum pool size and a maximum timeout for waiting for old connections to be released to the pool.

To set up a pooled connection to a single MongoDB instance:

ruby @client ="localhost", 27017, :pool_size => 5, :pool_timeout => 5)

Though the pooling architecture will undoubtedly evolve, it currently owes much credit to the connection pooling implementations in ActiveRecord and PyMongo.


Certain Ruby application servers work by forking, and it has long been necessary to re-establish the child process’s connection to the database after fork. But with the release of v1.3.0, the Ruby driver detects forking and reconnects automatically.

Environment variable MONGODB_URI

Mongo::MongoClient.from_uri, and will use ENV["MONGODB_URI"] if no other args are provided.

The URI must fit this specification:


If the type of connection (direct or replica set) should be determined entirely from ENV["MONGODB_URI"], you may want to use Mongo::MongoClient.from_uri because it will return either Mongo::MongoClient or a Mongo::MongoReplicaSetClient depending on how many hosts are specified. Trying to use with multiple hosts in ENV["MONGODB_URI"] will raise an exception.

String Encoding

The BSON (“Binary JSON”) format used to communicate with Mongo requires that strings be UTF-8 (

Ruby 1.9 has built-in character encoding support. All strings sent to Mongo and received from Mongo are converted to UTF-8 when necessary, and strings read from Mongo will have their character encodings set to UTF-8.

When used with Ruby 1.8, the bytes in each string are written to and read from Mongo as is. If the string is ASCII, all is well, because ASCII is a subset of UTF-8. If the string is not ASCII, it may not be a well-formed UTF-8 string.

Primary Keys

The _id field is a primary key. It is treated specially by the database, and its use makes many operations more efficient. The value of an _id may be of any type. The database itself inserts an _id value if none is specified when a record is inserted.

Primary Key Factories

A primary key factory is a class you supply to a DB object that knows how to generate _id values. If you want to control _id values or even their types, using a PK factory lets you do so.

You can tell the Ruby Mongo driver how to create primary keys by passing in the :pk option to the MongoClient#db method.

ruby include Mongo db ='localhost', 27017).db('dbname', :pk =>

A primary key factory object must respond to :create_pk, which should take a hash and return a hash which merges the original hash with any primary key fields the factory wishes to inject.

NOTE: if the object already has a primary key, the factory should not inject a new key; this means that the object may already exist in the database. The idea here is that whenever a record is inserted, the :pk object’s +create_pk+ method will be called and the new hash returned will be inserted.

Here is a sample primary key factory, taken from the tests:

ruby class TestPKFactory def create_pk(doc) doc['_id'] ||= doc end end

Here’s a slightly more sophisticated one that handles both symbol and string keys. This is the PKFactory that comes with the MongoRecord code (an ActiveRecord-like framework for non-Rails apps) and the AR Mongo adapter code (for Rails):

ruby class PKFactory def create_pk(doc) return doc if doc[:_id] doc.delete(:_id) # in case it exists but the value is nil doc['_id'] ||= doc end end

A database’s PK factory object may be set either when a DB object is created or immediately after you obtain it, but only once. The only reason it is changeable at all is so that libraries such as MongoRecord that use this driver can set the PK factory after obtaining the database but before using it for the first time.

The DB Class

Strict mode

NOTE: Support for strict mode has been deprecated and will be removed in version 2.0 of the driver.

Each database has an optional strict mode. If strict mode is on, then asking for a collection that does not exist will raise an error, as will asking to create a collection that already exists. Note that both these operations are completely harmless; strict mode is a programmer convenience only.

To turn on strict mode, either pass in :strict => true when obtaining a DB object or call the :strict= method:

ruby db ='localhost', 27017).db('dbname', :strict => true) # I'm feeling lax db.strict = false # No, I'm not! db.strict = true

The method DB#strict? returns the current value of that flag.



Socket timeouts

The Ruby driver support timeouts on socket read operations. To enable them, set the :op_timeout option when you create a Mongo::MongoClient object.

If implementing higher-level timeouts, using tools like Rack::Timeout, it’s very important to call Mongo::MongoClient#close to prevent the subsequent operation from receiving the previous request.


Before running the tests, make sure you install all test dependencies by running:

sh $ gem install bundler; bundle install

To run all default test suites (without the BSON extensions) just type:

sh $ rake test

If you want to run the default test suite using the BSON extensions:

sh $ rake test:ext

These will run both unit and functional tests. To run these tests alone:

sh $ rake test:unit $ rake test:functional

To run any individual rake tasks with the BSON extension disabled, just pass BSON_EXT_DISABLED=true to the task:

sh $ rake test:unit BSON_EXT_DISABLED=true

If you want to test replica set, you can run the following task:

sh $ rake test:replica_set

To run a single test at the top level, add -Itest since we no longer modify LOAD_PATH:

sh $ ruby -Itest -Ilib test/bson/bson_test.rb

To run a single test from the test directory, add -I. since we no longer modify LOAD_PATH:

sh $ ruby -I. -I../lib bson/bson_test.rb

To run a single test from its subdirectory, add -I.. since we no longer modify LOAD_PATH:

sh $ ruby -I.. -I../../lib bson_test.rb

To fix the following error on Mac OS X - “/…/lib/bson_ext/cbson.bundle: [BUG] Segmentation fault”:

sh $ rake compile

Release Notes

See history.


See credits.


Copyright (C) 2008-2013 10gen Inc.

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.