MongoUser Guide


Mongo is a pure Fantom driver for MongoDB v3.2+.

Mongo driver features:

  • Compatible with MongoDB v3.2+
  • Standard and capped collections
  • Pooled connection manager for multi-threaded use and automatic connection fail over.
  • Write commands: insert(), update(), delete() and findAndModify()
  • Optimised queries for findOne() and findAll()
  • Aggregation commands: aggregate(), distinct(), group() and mapReduce()
  • Index support: create(), ensure() and drop()
  • User support: create(), drop(), grant() and revoke() roles
  • Server side eval() commands
  • Database authentication
  • Cursor support
  • Write concern support
  • Text indexes and text searching
  • Support for Replica Set connection URLs

Mongo driver has been written specifically for MongoDB v3.2 or newer.

ALIEN-AID: See Morphia for a complete Fantom to MongoDB object mapping library!

Quick Start

  1. Start up an instance of MongoDB:
    C:\> mongod
    MongoDB starting
    db version v3.2.10
    waiting for connections on port 27017
  2. Create a text file called
    using afBson
    using afMongo
    using concurrent
    class Example {
        Void main() {
            mongoClient := MongoClient(ActorPool(), `mongodb://localhost:27017`)
            collection  := mongoClient.db("friends").collection("birds")
            documentIn  := [
                "_id"   : ObjectId(),
                "name"  : "Emma",
                "score" : 9
            emma   := collection.findAll.first
            result := PrettyPrinter { it.maxWidth = 20 }.print(emma)
  3. Run as a Fantom script from the command line:
    C:\> fan
      _____ ___ ___ ___ ___
     |     | . |   | . | . |
     |_|_|_|___|_|_|_  |___|
    Connected to MongoDB v3.2.10 (at mongodb://localhost:27017)
      "_id"   : ObjectId("57fe499fa81320d933000001"),
      "name"  : "Emma"
      "score" : 9,


MongoClient is the main entry point into Mongo. From there you can access all other components of MongoDB, namely Database, Collection, Index and User.

 `-- Database
      +-- Collection
      |    `-- Index
      `-- User


MongoClient is created with a ConnectionManager, which manages your connections to MongoDB. Use ConnectionManagerPooled for normal multi-threaded use:

conMgr := ConnectionManagerPooled(ActorPool(), `mongodb://localhost:27017`)
client := MongoClient(conMgr)

When you create a MongoClient it immediately connects to MongoDB and verifies the version:

.    Alien-Factory
 _____ ___ ___ ___ ___
|     | . |   | . | . |
|_|_|_|___|_|_|_  |___|

Connected to MongoDB v3.2.10

Note that ConnectionManagerPooled will always query the supplied MongoDB host(s) to find the primary node, on which all read and write operations are performed.


Mongo and MongoDB work with documents, they are used throughout the Mongo API. A MongoDB document is represented in Fantom as a Map of type [Str:Obj?]. All document keys must be strings. Document values can be any valid BSON type.

A MongoDB database stores documents in collections. Use the find() methods to query a collection. Using the friends database in the QuickStart Example we could do:

collection.findOne( ["name":"Emma"] )       // --> return the doc where 'name == Emma'
                                            //     ('Emma' must be unique)

collection.findAll                          // --> return ALL docs in the collection
collection.findAll( ["name":"Emma"] )       // --> return all docs where 'name == Emma'
collection.findAll( ["score": ["\$gt":7]] ) // --> return all docs with 'score > 7'

The $gt expression is an example of a Query operator.

To iterate over a massive collection without loading it all into memory, use a Cursor. Cursors download documents in batches, behind the scenes, as and when required. Create and use a Cursors by using the find() method:

collection.find( ["score": ["\$gt":2]] ) |cursor| {
    cursor.batchSize = 10

    while (cursor.hasNext)
        doc :=

Write Commands

The insert() command is simple enough and is demonstrated in the QuickStart example.

update() and delete() are similar in that they both take a query that describes which document(s) are to be updated / deleted. For most usages this will a simply be the id of the document in question:

collection.update( ["_id": objId], [ doc...] )

Note that as of MongoDB v2.6 there is longer any need to call a getLastError() function. All error handling is done via write concerns. By default Mongo will throw a MongoErr should a write error occur.


All documents held in a collection need a unique id, held in a field named _id. If the _id field does not exist, MongoDB will create one for you of type ObjectId.

Note that _id does not need to an ObjectId, it can be any BSON type. It just needs to be unique in the collection.

Like marmite, people tend to have a love / hate relationship with the ObjectId. The good comments revolve around it having a natural sort that (roughly) corresponds to creation time. The bad is that it's a large human-unfriendly 24 char identifier, and in humongous collections it eats up precious bytes which means the index may not fit into RAM.


To set a default user to be used by all connections, set the username and password in the MongoDB connection URL:

conMgr := ConnectionManagerPooled(ActorPool(), `mongodb://<username>:<password>@localhost:27017`)
client := MongoClient(conMgr)

Another way, that may also be used in conjunction with URL credentials, is to use an authenticated connection. Authenticated connections are bound to the database they are authenticated against.

client := MongoClient(conMgr)
db     := client["database"]
data   := db.authenticate("ZeroCool", "password") |authDb -> Obj?| {
    return authDb["top-secret"].findAll

All Mongo objects ( Collection, Index, User, etc...) created from the authenticated database will inherit the user credentials. Note that the database must be accessed via the authDb variable for the commands to be authenticated.

Note that authentication defaults to SCRAM-SHA-1 but basic MONGODB-CR is also supported.

Connection Fail Over

The PooledConnectionManager accepts a replica set URL with multiple hosts (with optional ports):


When startup() is called, the hosts are queried to find the primary / master node. All read and write operations are then performed on this primary node.

When a connection to the master node is lost, all hosts are automatically re-queried to find a new master.


The Alien-Factory MongoDB driver was inspired by fantomongo by Liam Staskawicz.

If you're looking for cross-platform MongoDB GUI client then look no further than Robomongo!