require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'

  gem 'mongoid', '~> 8.1.0'
end

Mongoid.configure do |config|
  config.clients.default = {
    hosts: ['mongo:27017'],
    database: 'mongoid_test',
  }
end
Mongoid.purge!

class Category
  include Mongoid::Document

  has_many :articles
end

class Article
  include Mongoid::Document

  field :body, type: String

  belongs_to :category
end

category = Category.create!
1000.times do |i|
  Article.create!(body: "Article #{i}", category: category)
end

puts Benchmark.bm do |x|
  Mongoid::Config.legacy_pluck_distinct = true
  x.report('legacy_pluck_distinct enabled') { 100.times { category.articles.distinct(:id) } }
  Mongoid::Config.legacy_pluck_distinct = false
  x.report('legacy_pluck_distinct disabled') { 100.times { category.articles.distinct(:id) } }

  context = category.articles.context
  name = '_id'

  # Instanciate `field` only once
  x.report('field found once') do
    100.times do
      field = Article.traverse_association_tree(name)
      context.view.distinct(name).map do |value|
        context.send(:demongoize_with_field, field, value, false)
      end
    end
  end

  # Instanciate `field` for each record
  x.report('field found for each record') do
    100.times do
      context.view.distinct(name).map do |value|
        field = Article.traverse_association_tree(name)
        context.send(:demongoize_with_field, field, value, false)
      end
    end
  end
end

                                    user     system      total        real
legacy_pluck_distinct enabled   0.092737   0.005985   0.098722 (  0.175196)
legacy_pluck_distinct disabled  0.212732   0.002981   0.215713 (  0.298624)
field found once                0.102693   0.001005   0.103698 (  0.178545)
field found for each record     0.167417   0.003969   0.171386 (  0.246786)