Build Status


  • Supports MongoDB versions 3.0, 3.2, 3.4, 3.6, 4.0
  • Connection pooling (through db_connection)
  • Streaming cursors
  • Performant ObjectID generation
  • Follows driver specification set by 10gen
  • Safe (by default) and unsafe writes
  • Aggregation pipeline
  • Replica sets

Immediate Roadmap

  • Make sure requests don’t go over the 16mb limit
  • New 2.6 write queries and bulk writes

Tentative Roadmap

  • Use meta-driver test suite
  • Server selection / Read preference


Data representation

BSON                Elixir
----------          ------
double              0.0
string              "Elixir"
document            [{"key", "value"}] | %{"key" => "value"} (1)
binary              %BSON.Binary{binary: <<42, 43>>, subtype: :generic}
object id           %BSON.ObjectId{value: <<...>>}
boolean             true | false
UTC datetime        %DateTime{}
null                nil
regex               %BSON.Regex{pattern: "..."}
JavaScript          %BSON.JavaScript{code: "..."}
integer             42
symbol              "foo" (2)
min key             :BSON_min
max key             :BSON_max

1) Since BSON documents are ordered Elixir maps cannot be used to fully represent them. This driver chose to accept both maps and lists of key-value pairs when encoding but will only decode documents to lists. This has the side-effect that it’s impossible to discern empty arrays from empty documents. Additionally the driver will accept both atoms and strings for document keys but will only decode to strings.

2) BSON symbols can only be decoded.



Add mongodb to your mix.exs deps and :applications (replace >= 0.0.0 in deps if you want a specific version). Mongodb supports the same pooling libraries db_connection does (currently: no pooling, poolboy, and sbroker). If you want to use poolboy as pooling library you should set up your project like this:

def application do
  [applications: [:mongodb, :poolboy]]

defp deps do
  [{:mongodb, ">= 0.0.0"},
   {:poolboy, ">= 0.0.0"}]

Then run mix deps.get to fetch dependencies.

Connection pooling

By default mongodb will start a single connection, but it also supports pooling with the :pool option. For poolboy add the pool: DBConnection.Poolboy option to Mongo.start_link and to all function calls in Mongo using the pool.

# Starts an unpooled connection
{:ok, conn} = Mongo.start_link(url: "mongodb://localhost:27017/db-name")

# Gets an enumerable cursor for the results
cursor = Mongo.find(conn, "test-collection", %{})

|> Enum.to_list()
|> IO.inspect

If you’re using pooling it is recommend to add it to your application supervisor:

def start(_type, _args) do
  import Supervisor.Spec

  children = [
    worker(Mongo, [[name: :mongo, database: "test", pool: DBConnection.Poolboy]])

  opts = [strategy: :one_for_one, name: MyApp.Supervisor]
  Supervisor.start_link(children, opts)

Then you can use the pool as following:

Mongo.find(:mongo, "collection", %{}, limit: 20, pool: DBConnection.Poolboy)

Replica Sets

To connect to a Mongo cluster that is using replica sets, it is recommended to use the :seeds list instead of a :hostname and :port pair.

{:ok, pid} = Mongo.start_link(database: "test", seeds: ["", ""])

This will allow for scenarios where the first "" is unreachable for any reason and will automatically try to connect to each of the following entries in the list to connect to the cluster.


Using $and

Mongo.find(:mongo, "users", %{"$and" => [%{email: ""}, %{first_name: "first_name"}]})

Using $or

Mongo.find(:mongo, "users", %{"$or" => [%{email: ""}, %{first_name: "first_name"}]})

Using $in

Mongo.find(:mongo, "users", %{email: %{"$in" => ["", ""]}})


The SSL test suite is enabled by default. You have two options. Either exclude the SSL tests or enable SSL on your Mongo server.

Disable the SSL tests

mix test --exclude ssl

Enable SSL on your Mongo server

$ openssl req -newkey rsa:2048 -new -x509 -days 365 -nodes -out mongodb-cert.crt -keyout mongodb-cert.key
$ cat mongodb-cert.key mongodb-cert.crt > mongodb.pem
$ mongod --sslMode allowSSL --sslPEMKeyFile /path/to/mongodb.pem
  • For --sslMode you can use one of allowSSL or preferSSL
  • You can enable any other options you want when starting mongod


Copyright 2015 Justin Wood

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.