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CongoMongo Build Status


A toolkit for using MongoDB with Clojure.

This library is a pretty lightweight wrapper around the MongoDB Java driver. If you are starting a new project and looking for a more complete package including validation, better documentation and more it is a good idea to also look at Monger.

Releases and Dependency Information

Latest stable release is 2.1.0.

Leiningen dependency information:

[congomongo "2.1.0"]

Clojure CLI:

congomongo {:mvn/version "2.1.0"}

Maven dependency information:


Gradle dependency information:

compile 'congomongo:congomongo:2.1.0'




(ns my-mongo-app
  (:require [somnium.congomongo :as m]))

make a connection using array of hosts

(def conn
  (m/make-connection "mydb"
                     :instances [{:host "" :port 27017}]))
=> #'user/conn

conn => {:mongo #<MongoClient Mongo: />, :db #<DBApiLayer mydb>}

or using a mongodb uri

(def conn
  (m/make-connection "mongodb://"))
=> #'user/conn

conn => {:mongo #<MongoClient Mongo: />, :db #<DBApiLayer mydb>}

set the connection globally

(m/set-connection! conn)

or locally

(m/with-mongo conn
    (m/insert! :robots {:name "robby"}))

close the connection

(m/close-connection conn)

specify a write concern

(m/set-write-concern conn :journaled)

These are the official write concerns, more details about them can be found in the WriteConcern javadoc.

  • :unacknowledged will report network errors - but does not wait for the write to be acknowledged
  • :acknowledged will report key constraint and other errors - this is the default
  • :journaled waits until the primary has sync'd the write to the journal
  • :fsynced waits until a write is sync'd to the filesystem
  • :replica-acknowledged waits until a write is sync'd to at least one replica as well
  • :majority waits until a write is sync'd to a majority of replica nodes

specify a read preference

You can pass a simple read preference (without tags) to each function accepting read preferences. This may look like:

(m/fetch :fruit :read-preference :nearest)

to get the fruit from the nearest server. You may create more advances read preferences using the read-preference function.

(let [p (m/read-preference :nearest {:location "Europe"})]
   (fetch :fruit :read-preference p)

to be more specific to get the nearest fruit. You may also set a default ReadPreference on a per collection or connection basis using set-read-preference or set-collection-read-preference!.

(m/set-read-preference conn :primary-preferred)
(m/set-collection-read-preference! :news :secondary)

Simple Tasks


(m/insert! :robots
           {:name "robby"})


(def my-robot (m/fetch-one :robots)) => #'user/my-robot

my-robot => {:name "robby",
             :_id  #<ObjectId> "0c23396f7e53e34a4c8cf400">}


(m/update! :robots my-robot (merge my-robot {:name "asimo"}))

=>  #<WriteResult { "serverUsed" : "/" ,
                    "updatedExisting" : true ,
                    "n" : 1 ,
                    "connectionId" : 169 ,
                    "err" :  null  ,
                    "ok" : 1.0}>


(m/destroy! :robots {:name "asimo"}) => #<WriteResult { "serverUsed" : "/" ,
                                                        "n" : 1 ,
                                                        "connectionId" : 170 ,
                                                        "err" :  null  ,
                                                        "ok" : 1.0}>
(m/fetch :robots) => ()

More Sophisticated Tasks

mass inserts

(dorun (m/mass-insert!
         (for [x (range 100) y (range 100)]
           {:x x
            :y y
            :z (* x y)}))

=> nil ;; without dorun this would produce a WriteResult with 10,000 maps in it!

(m/fetch-count :points)
=> 10000

ad-hoc queries

  :where {:x {:$gt 10
              :$lt 20}
          :y 42
          :z {:$gt 500}})

=> {:x 12, :y 42, :z 504, :_id ... }

aggregation (requires mongodb 2.2 or later)

  {:$match {:type "airfare"}}
  {:$project {:department 1, :amount 1}}
  {:$group {:_id "$department", :average {:$avg "$amount"}}})

=> {:serverUsed "...", :result [{:_id ... :average ...} {:_id ... :average ...} ...], :ok 1.0}

This pipeline of operations selects expenses with type = 'airfare', passes just the department and amount fields thru, and groups by department with an average for each.

Based on 10gen's Java Driver example of aggregation.

The aggregate function accepts any number of pipeline operations.


(m/authenticate conn "myusername" "my password")

=> true

advanced initialization using mongo-options

(m/make-connection :mydb
                   :instances [{:host ""}]
                   :options (m/mongo-options :auto-connect-retry true))

The available options are hyphen-separated lowercase keyword versions of the camelCase options supported by the Java driver. Prior to CongoMongo 0.4.0, the options matched the fields in the MongoOptions class. As of CongoMongo 0.4.0, the options match the method names in the MongoClientOptions class instead (and an IllegalArgumentException will be thrown if you use an illegal option). The full list (with the 2.10.1 Java driver) is:

(:auto-connect-retry :connect-timeout :connections-per-host :cursor-finalizer-enabled
 :db-decoder-factory :db-encoder-factory :description :legacy-defaults
 :max-auto-connect-retry-time :max-wait-time :read-preference :socket-factory
 :socket-keep-alive :socket-timeout :threads-allowed-to-block-for-connection-multiplier

initialization using a Mongo URI

(m/make-connection "mongodb://user:pass@host:27071/databasename")
;; note that authentication is handled when given a user:pass@ section

;; or using SRV DNS service detection
(m/make-connection "mongodb+srv://user:pass@mymongocluster/databasename")

A query string may also be specified containing the options supported by the MongoClientURI class.

easy json

(m/fetch-one :points
             :as :json)

=> "{ \"_id\" : \"0c23396ffe79e34a508cf400\" ,
      \"x\" : 0 , \"y\" : 0 , \"z\" : 0 }"

custom type conversions

For example, use Joda types for dates:

(extend-protocol somnium.congomongo.coerce.ConvertibleFromMongo
  (mongo->clojure [^java.util.Date d keywordize] (new org.joda.time.DateTime d)))

(extend-protocol somnium.congomongo.coerce.ConvertibleToMongo
  (clojure->mongo [^org.joda.time.DateTime dt] (.toDate dt)))


Use :explain? on fetch to get performance information about a query. Returns a map of statistics about the query, not rows:

(m/fetch :users :where {:login "alice"} :explain? true)
{:nscannedObjects 2281,
 :nYields 0,
 :nscanned 2281,
 :millis 2,
 :isMultiKey false,
 :cursor "BasicCursor",
 :n 1,
 :indexOnly false,
 :allPlans [{:cursor "BasicCursor", :indexBounds {}}],
 :nChunkSkips 0,
 :indexBounds {},
 :oldPlan {:cursor "BasicCursor", :indexBounds {}}}

default query options

Sometimes it's very helpful to be able to provide default options for all queries (for example, specify default max-time-ms timeout) instead of specifying it for each call. You can do this by wrapping your code in the with-default-query-options macro. Options specified in a particular call will have a priority and overwrite default-query-options.

; This call will only return one item, since it is using the default options
(with-default-query-options {:limit 1}
  (fetch :thingies :where {:foo 1}))

; You can also override the defaults by specifying a new value
(with-default-query-options {:limit 1}
  (fetch :thingies :where {:foo 1} :limit 2)) ; returns 2 items

Developer information

Change Log

Version 2.1.0 - Nov 25, 2019

Adds support for setting default query options, see documentation above.

Version 2.0.0 - Nov 22, 2019

BREAKING CHANGES IN THIS RELEASE! The group, eval and geoNear commands have been deprecated for a long while now and were finally removed in MongoDB 4.2. They have now been removed from this library as well. You are recommended to use the aggregate command to replace the functionality of group and geoNear.

Version 1.1.0 - Apr 8, 2019

Added ability to specify timeout for fetch and fetch-and-modify operations.

Version 1.0.1 - Sep 11, 2018

Fixed bug where too few documents were returned if fetching with a limit that was larger than the default batch size.

Version 1.0.0 - Sep 11, 2018

Updated to support mongo-java-driver 3.0+ which enables use of TLS connections and DNS SRV connection strings. Authentication has changed significantly in the 3.0 driver which necessitated some breaking API changes around connecting and authenticating.


  • Usernames and passwords for authenticated connections must be supplied to make-connection rather than authenticating after the connection has been created. The make-connection API has been changed to accomodate this. Optional parameters (instances, Mongo options, username and password) are now passed via keyword args.
  • The authenticate function has been removed.
  • The deprecated mongo! function has been removed. Use (set-connection (make-connection ...))

Version 0.5.3 - Aug 30, 2018

  • Add new option :partial-filter-expression to add-index! in order to support partial indexes.

Version 0.5.2 - May 2, 2018

  • Make aggregate method compatible with MongoDB 3.6

Version 0.5.1 - Jan 19, 2018

  • Add support for setting _id when creating GridFS files
  • Update Java driver to 2.14.2

Version 0.5.0 - Jun 6, 2016

  • DROP SUPPORT FOR CLOJURE 1.3.0! CongoMongo 0.5.0 onward no longer supports Clojure 1.3.0 or earlier. For Clojure 1.3.0, use CongoMongo 0.3.0 thru 0.4.8. CongoMongo 0.4.8 is the last release that supports Clojure 1.3.0. For Clojure 1.2.1 and earlier, use CongoMongo 0.2.3 or earlier. CongoMongo 0.2.3 is the last release that supports Clojure 1.2.x.
  • Add Clojure 1.9.0 compatibility (handling of seqable? in coerce namespace) - issue #147
  • Clojure is now a "provided" dependency and should no longer appear as a transitive dependency in projects that use CongoMongo, making it easier to get rid of conflicts! Potentially a breaking change if a project depended on CongoMongo but did not have an explicit dependency on Clojure itself.

Version 0.4.8 - Feb 25, 2016

  • Update to 0.2.6
  • Update default Clojure version to 1.8.0 and update test-all alias
  • Rename update test to update-one to avoid Clojure update name conflict

Version 0.4.7 - Dec 27, 2015

  • Update Java driver to 2.14.0

Version 0.4.6 - Jul 29, 2015

  • Add support for hints on fetches
  • Error on unsupported arguments (eg read-preferences on fetch-one)

Version 0.4.5 - Jul 18, 2015

  • update Java driver to 2.13.2
  • change default Clojure version from 1.6.0 to 1.7.0 (we still support back to 1.3.0)

Version 0.4.4 - April 29, 2014

  • update Java driver to 2.12.1

Version 0.4.3 - April 8, 2014

  • change default Clojure version from 1.5.1 to 1.6.0 (we still support back to 1.3.0)
  • update Java driver to 2.12.0 to support MongoDB 2.6.0
  • support :write-concern on mass-insert!

Version 0.4.2 - February 25, 2014

  • change default Clojure version from 1.4 to 1.5.1 and add test coverage for 1.6.0-beta1
  • fix set insertion test for Clojure 1.6
  • fix docstring (#130 dwwoelfel)
  • fix reflection warnings (#123 niclasmeier)

Version 0.4.1 - March 14, 2013

  • read preference supported (per-connection, per-collection, per-fetch (#122 niclasmeier)
  • add-index! supports :background true/false (#121 dwwoelfel)
  • namespaced keyword keys in maps are roundtripped correctly (#120 AdamClements)

Version 0.4.0 - January 4, 2013


10gen have updated all their drivers to be more consistent in naming. They have also changed the default write concern (from :none to :normal, effectively). The new classes introduced have different APIs to the classes they replace so there are some knock on changes to CongoMongo as well. The biggest changes are that opt! has been removed and the actual keyword arguments for MongoOptions have changed to match MongoClientOptions$Builder instead. An IllegalArgumentException is thrown for unknown arguments now.

  • You can now pass :write-concern to destroy!, insert! and update! #74
  • Upgrade to 2.10.1 Java driver (#104)
    • Switches from Mongo to MongoClient
    • Switches from MongoURI to MongoClientURI
    • Switches from MongoOptions to MongoClientOptions
    • Adds seven new write concern names - the old names are deprecated (see set-write-concern below)
    • Changes the default write concern from :unacknowledged (formerly called :normal) to :acknowledged (formerly called :safe or :strict)
  • Update to 0.2.1 (as part of #104)
  • Add :replicas-safe write concern (although it is deprecated)
  • Add support for :explain? (#102, #103 arohner)
  • Switch fetch to use non-deprecated APIs (#101 arohner)

Version 0.3.3 - November 2nd, 2012

  • Add dbobject and coerce-ordered-fields to support multi-column sorting (#100)
    • Deprecate coerce-index-fields in favor of coerce-ordered-fields

Version 0.3.2 - October 30th, 2012

  • Update Java driver to 2.9.3 for recommended update (#99)

Version 0.3.1 - October 23rd, 2012

  • Update Java driver to 2.9.2 for CRITICAL update (#98)

Version 0.3.0 - October 23rd, 2012

  • Update to 0.2.0 (#97)
  • Update clojure.core.incubator to 0.1.2

Version 0.2.3 - October 30th, 2012 - last release to support Clojure 1.2.x!

  • Update Java driver to 2.9.3 for recommended update (#99)

Version 0.2.2 - October 23rd, 2012

  • Update Java driver to 2.9.2 for CRITICAL update (#98)

Version 0.2.1 - October 23rd, 2012

  • Support insertion of sets (#94, #95)
  • Declare MongoDB service for Travis CI (#96)

Version 0.2.0 - October 10th, 2012:

  • Added URL / license / mailing list information to project.clj so it will show up in Clojars and provide a better user experience
  • Allow make-connection to accept symbols again (#80, fixes issue introduced in #79)
  • Prevent fetch one / sort being used together (#81)
  • Remove :force option from add-index! since it is no longer effective (#82, #83)
  • Add :sparse option to add-index! (#84)
  • Upgrade to 2.9.1 Java driver (#85, #89)
  • Upgrade project to use Clojure 1.4.0 as base version (#86, #88)
  • Upgrade project to use Leiningen 2 (#87)
  • Add aggregate function to leverage MongoDB 2.2 aggregation framework (#90)

Version 0.1.10 - July 31st, 2012:

  • Add support for MongoDB URI string in make-connection (#79)
  • Fix with-connection / with-db interaction (#75)

Version 0.1.9 - April 20th, 2012:

  • Bump data.json => 0.1.3
  • Bump multi test to 1.4.0 & 1.5.0-SNAPSHOT for Clojure
  • Add with-db macro (#53, #54)
  • Support vector :only in fetch-and-modify (to match fetch) (#65)
  • Add group aggregation (#66)
  • Allow insert! to respect previous set-write-concern call (#72)
  • Add :safe, :fsync-safe, :replica-safe write concerns (#72)
  • In order to get throw on error behavior, you must call set-write-concern with :safe or stricter!
  • Deprecate :strict - use :safe instead

Version 0.1.8:

  • adds fetch-by-ids (#44)
  • improves error handling when connection not set up (#42)
  • updates to 0.1.2 (for performance fixes)
  • numerous documentation fixes (#38, #39, #40, #41, #45)
  • update to 2.7.3 driver (#46, #48)
  • remove version ranges - make 1.3.0 the default Clojure version (#47 etc)
  • add multi-version testing
  • add Travis CI test hook

Version 0.1.7 adds the ability to create MongoOptions and pass them into make-connection as the last argument, so that you can control autoConnectRetry and timeouts and so on. This release also fixes a number of small bugs around type hints introduced in 0.1.6; corrects the upsert(?) parameter in fetch-and-modify; upgrades the Java driver to 2.6.5. The :only parameter can now be a map of field names and true / false values to allow fields to be included or excluded. The original vector of field names is still supported to include only the named fields.

Version 0.1.6 removes (almost) all of the reflection warnings.

Version 0.1.5 adds compatibility with Clojure 1.3, in addition to 1.2.

Congomongo 0.1.4 introduces support for MongoDB 1.8's modified map-reduce functionality, wherein the 'out' parameter is required. With this and future Congomongo releases, it will no longer be possible to access the map-reduce features of older MongoDB instances.

As of congomongo 0.1.3, Clojure 1.2 and Clojure-contrib 1.2 are required. If you need compatibility with Clojure 1.1, please stick with congomongo 0.1.2.

There is now a Google Group Come help us make ponies for great good.

Clojars group is congomongo.

License and copyright

Congomongo is made available under the terms of an MIT-style license. Please refer to the source code for the full text of this license and for copyright details.

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