mongo_default_comment_rails.rb

require "mongo/collection/view"

# Add default "comment" for every request to MongoDB.
# https://github.com/mongodb/mongo-ruby-driver/blob/master/lib/mongo/collection/view.rb#L132
Mongo::Collection::View.class_eval do
  alias :mongo_collection_view_initialize :initialize

  def initialize(collection, filter = {}, options = {})
    filter["$comment"] ||= default_comment
    mongo_collection_view_initialize(collection, filter, options)
  end

  private

  def default_comment
    @application_name ||= Rails.application.class.parent_name.downcase

    line = caller.find { |line| line.start_with?(Rails.root.to_s) && !line.start_with?(__FILE__) }
    line = line ? line.split('/')[-1] : "(console)"

    [@application_name, line].join("|")
  end
end