Gem Version Build Status RubyGems Code Climate Test Coverage

Allow you to pluck deeply into nested associations without loading a bunch of records.

And DRY up your code when using #as_json.


Add this line to your application's Gemfile:

gem 'deep_pluck'

And then execute:

$ bundle

Or install it yourself as:

$ gem install deep_pluck


Similar to #pluck method

User.deep_pluck(:id, :name)
# SELECT `users`.`id`, `users`.`name` FROM `users` 
# => [{'id' => 1, 'name' => 'David'}, {'id' => 2, 'name' => 'Jeremy'}]

Pluck deep into associations

User.deep_pluck(:name, :posts => :title)
# SELECT `users`.`id`, `users`.`name` FROM `users`
# SELECT `posts`.`user_id`, `posts`.`title` FROM `posts` WHERE `posts`.`user_id` IN (1, 2)
# => [
#  {'name' => 'David' , :posts => [{'title' => 'post1'}, {'title' => 'post2'}]}, 
#  {'name' => 'Jeremy', :posts => [{'title' => 'post3'}]}
# ]

DRY up Rails/ActiveRecord includes when using as_json

Assume the following relations:

User has_many Posts.
Post has_many PostComments.
User has_one Contact.

And the following #as_json example:

User.where(:name => %w(Pearl Kathenrie)).includes([{:posts => :post_comments}, :contact]).as_json({
  :root => false,
  :only => [:name, :email], 
  :include => {
    'posts' => {
      :only => :name, 
      :include => {
        'post_comments' => {
          :only => :comment,
    'contact' => {
      :only => :address,

It works as expected, but is not very DRY, repeat writing include, posts, post_comments so many times.

You could refactor it with #deep_pluck like:

User.where(:name => %w(Pearl Kathenrie)).deep_pluck(
  'posts' => [:name, 'post_comments' => :comment], 
  'contact' => :address,

Better Performance

deep_pluck return raw hash data without loading a bunch of records.

In that faster than #as_json, or #select.

The following is the benchmark test on 3 users, 6 posts, where users table have 14 columns and posts have 6 columns. As it shows, deep_pluck is 4x faster than as_json.

# Repeat 500 times
# User.includes(:posts).as_json(:only => :email, :include => {:posts => {:only => :title}})
# User.deep_pluck(:email, {'posts' => :title})

                       user     system      total        real
as_json            1.740000   1.230000   2.970000 (  3.231465)
deep_pluck         0.660000   0.030000   0.690000 (  0.880018)

The following is the benchmark test on 10000 users, where users table have 46 columns. As it shows, deep_pluck is 40x faster than as_json and 4x faster than map.

# Repeat 1 times
#'account, email').map{|s| {'account' => s.account, 'email' =>}}
#'account, email').as_json(:only => [:account, :email])
# User.deep_pluck(:account, :email)

                       user     system      total        real
map                0.210000   0.000000   0.210000 (  0.225421)
as_json            1.980000   0.060000   2.040000 (  2.042205)
deep_pluck         0.040000   0.000000   0.040000 (  0.051673)


After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.