Using Mongoid in Ruby applications outside of Rails

Mongoid and MongoMapper are two Ruby ODM (Object Document Mapper) gems for the Mongo database.

I've used both to a limited extent and they seem comparable for my needs. Mongoid seems to be getting a bit more traction than MongoMapper and it certainly has better docs.

My current project uses Mongo in a standalone Ruby application - no Rails in sight - but the docs are almost totally focused on Rails. Here is how you use Mongoid outside of Rails.

I'm storing relevant RSS entries in the database. My model looks something like this (heavily truncated):

class RssEntry
  include Mongoid::Document

  field :entry_id
  field :title
  field :authors, :type => Array
  field :timestamp, :type => Time

  index :timestamp
  index :title
end

Be sure and define your indexes carefully for fields that you want to search on, otherwise Mongo will run out of memory when searching even modest datasets. I see this as a weakness of the database. See important note on creating indexes below!

and the application looks a bit like this (edited):

#!/usr/bin/env ruby
require 'mongoid'
$:.unshift File.dirname(__FILE__)
require 'mongoid_test_model'

Mongoid.configure do |config|
  name = "mongoid_test_db"
  host = "localhost"
  port = 27017
  config.database = Mongo::Connection.new.db(name)
end
[...]
entry = RssEntry.create({
    :title => title,
    :entry_id => id,
    :authors => authors,
    :timestamp = Time.new
})

And if you are using the defaults of localhost and 27017 then you can leave those definitions out.

NOTE: Simply defining an index in your model is NOT enough. You have to explicitly create the index. When you use Mongoid with Rails it sets up a rake task so you can run 'rake db:create_indexes' but outside of that environment you need to do this yourself.

You'll want to write a simple script/rake task to set this up, in which you call create_indexes on EACH class in your model that uses Mongoid. For example:

#!/usr/bin/env ruby
require 'mongoid'
$:.unshift File.dirname(__FILE__)
require 'mongoid_test_model'

Mongoid.configure do |config|
  name = "mongoid_test"
  host = "localhost"
  port = 27017
  config.database = Mongo::Connection.new.db(name)
end

# Call on each of the relevant models
RssEntry.create_indexes()

Previously, you could specify auto-indexing within your models but this has now be deprecated or removed, so ignore any references to that.