convert_ids.rb

# with multiple collections + commands for renaming back the collections

require 'mongo'

# Stop writing to your database.
# Then, for each collection:
# Specify the DB and COLLECTION you want to convert.
# Will insert all modified documents into a new collection
# called 'new_' + old_collection_name.
# Then you can delete the old collection and rename the new one
# once you've verified that the new collection is correct.

DB = "" # Put your db name here

COLLECTIONS = [] # Put a list of collection names here

def convert_ids(obj)
  if obj.is_a?(String) && obj =~ /^[a-f0-9]{24}$/
    BSON::ObjectID(obj)
  elsif obj.is_a?(Array)
    obj.map do |v|
      convert_ids(v)
    end
  elsif obj.is_a?(Hash)
    obj.each do |k, v|
      obj[k] = convert_ids(v)
    end
  else
    obj
  end
end

def convert_collection collection
  original_collection = @db[collection]
  new_collection = @db['new_' + collection]
  
  puts "db.#{collection}.renameCollection('#{original_collection.name}_original')"
  puts "db.new_#{collection}.renameCollection('#{original_collection.name}')"
  new_collection.drop
  
  original_collection.find({}, :timeout => false, :sort => "_id") do |c|
    c.each do |doc|
      new_doc = convert_ids(doc)
      new_collection.insert(new_doc, :safe => true)
    end
  end
end

@con = Mongo::Connection.new
@db = @con[DB]

COLLECTIONS.each do |collection|
  convert_collection collection
end

Thanks. We'll just keep your version here so that people have a few different examples.

Kyle