Rails Integration

Mongoid seamlessly integrates into Ruby on Rails applications. This page describes features that are automatically enabled in the context of a Rails application and Rails-related functionality which can be manually enabled.


You can set Mongoid configuration options in your application.rb along with other Rails environment specific options by accessing config.mongoid. The mongoid:config generator will create an initializer in config/initializers/mongoid.rb which can also be used for configuring Mongoid. Note, though, that options set in your config/mongoid.yml will take precedence over options set elsewhere; it is recommended that whenever possible you use mongoid.yml as the default location for Mongoid configuration.

module MyApplication
  class Application < Rails::Application
    config.mongoid.logger = Logger.new(STDERR, :warn)

Model Preloading

In order to properly set up single collection inheritance, Mongoid needs to preload all models before every request in development mode. This can get slow, so if you are not using any inheritance it is recommended you turn this feature off.

config.mongoid.preload_models = false


Similarly to ActiveRecord, Mongoid configures Rails to automatically convert certain exceptions to well-known HTTP status codes, as follows:

Mongoid::Errors::DocumentNotFound : 404
Mongoid::Errors::Validations : 422

Controller Runtime Instrumentation

Mongoid provides time spent executing MongoDB commands (obtained via a driver command monitoring subscription) to Rails' instrumentation event process_action.action_controller. This time is logged together with view time like so:

Completed 200 OK in 2739ms (Views: 12.6ms | MongoDB: 0.2ms)

This logging is set up automatically.

Note: the time indicated is the time taken by MongoDB cluster to execute MongoDB operations, plus the time taken to send commands and receive results from MongoDB over the network. It does not include time taken by the driver and Mongoid to generate the queries or type cast and otherwise process the results.

Rake Tasks

Mongoid provides the following rake tasks when used in a Rails environment: