MongoLight

MongoLight is a lightweight object-relational mapper for Rails and MongoDB. It is not ActiveRecord compatible. Rather, the primary purpose is to be a thin wrapper around the excellent core MongoDB driver.

The only Rails dependency is on ActiveSupport::Concern.

The wrapper fits a specific use-case (mine).

Setup

Configure MongoLight via MongoLight.configure:

MongoLight.configure do |config|
  config.connection = Mongo::Connection.new
  config.database = 'mongolight_tests'
end

This'll automatically handle Passenger forking issues (if Passenger is running).

replica concern and testing

For safe writes, I like to use w:majority. However, MongoDB will raise an exception if you use this while not using replica sets. This can make testing code more of a pain than necessary. If you configure MongoLight with config.skip_replica_concern = true, then :w => X or :w => :majority will automatically be stripped when calling save(:w => majority) or save!(:w => 3). (For example, you could do config.skip_replica_concern = Rails.env.test?)

Documents

To define a document include MongoLight::Document and define your properties using the mongo_accessor method:

class User
	include MongoLight::Document
	mongo_accessor({:name => :name, password => :pw, :email => :e})
end

Within your code, you can access the name, password and email properties. However, internally, MongoDB will store the fields as name, pw and e (document databases store the field names with each document, this can save a lot of space (we saved 25%)).

Document Manipulation

Most of what you can do on a MongoDB collection (again, the Ruby driver), you can do on a MongoLight document:

#string ids which are valid BsonIds will automatically get converted
User.find_by_id(some_id)
User.find_one(hash_selector)
User.find(selector, options)
User.remove(selector)
User.update(selector, new_document, options)

In addition to any options which the ruby driver supports, the find method can be passed ``{:raw => true}` which'll cause a hash to be returned rather than a mapped object.

Instances can be saved via save or save! (safe mode).

New instances can be created by passing a hash into the constructor:

User.new({:name => 'goku', :password => 'over 9000!!!'})

Finally, you can always access the underlying collection from a class or object (User.collection or user.collection).

Embedded Documents

Embedded documents are supported. First, define an embedded document using include MongoLight::EmbeddedDocument and the same mongo_accessor method:

class Comment
	include MongoLight::EmbeddedDocument
	mongo_accessor({:title => :t, description => :d})
end

Next, use the following fancy syntax for your root document:

class User
	include MongoLight::Document
	mongo_accessor({:name => :name, password => :pw, :email => :e, :comment => {:field => :c, :class => Comment}})
end

Again, this'll make comments accessible on your objects, but store it within the c field.

If you want an array of embedded documents, simply specify :array => true:

...
:comments => {:field => :c, :class => Comment, array => true}})

Please note that aliasing completely fails when querying embedded documents - you need to use the shortened name:

User.find({:name => 'blah', 'c.t' => 'blah2}) #yes, it sucks