BulkLoader

# app/models/post.rb

class Post < ApplicationRecord
  include BulkLoader::DSL

  bulk_loader :comment_count, :id, default: 0 do |ids|
    Comment.where(id: ids).group(:post_id).count
  end
end

You can use this like followings:

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def index
    @posts = Post.limit(10)

    # load comment_count blocks with mapping by #id
    # you can avoid N+1 queries.
    Post.bulk_loader.load(:comment_count, @posts)

    render(json: @posts.map {|post| { id: post.id, comment_count: post.comment_count } })
  end
end

BulkLoader::DSL only create bulk_loader class method and bulk_loader method. So you can use with any object that is not ActiveRecord.

If you include BulkLoader::DSL, you can use bulk_loader class method.

class YourModel
  include BulkLoader::DSL

  bulk_loader :name, :mapped_key, default: nil do |mapped_keys|
    # something with mapped_keys
    {
      mapped_key => value, # you should return Hash that has mapped_key as key.
    }
  end
end

that create a instance method that name is :name.

mapped_key is Symbol or Proc. if you want to use original object, you can pass ->(your_model) { your_model } .

If block's result return Hash that cannot mapped to original object, you can return value using default option. If you does not pass default option, default is nil.

If you want to pass object like Array, you should use with lambda.

class YourModel
  include BulkLoader::DSL

  bulk_loader :name, :mapped_key, default: -> { [] } do |mapped_keys|
    # something with mapped_keys
    {
      mapped_key => value, # you should return Hash that has mapped_key as key.
    }
  end
end

:name method is just shorthand for bulk_loader.public_send(:name). So if you not want to create :name method, you can pass export: false to bulk_loader definition.

class YourModel
  include BulkLoader::DSL

  bulk_loader :name, :mapped_key, default: nil, export: false do |mapped_keys|
    # something with mapped_keys
  end
end

then you can use this like followings.

  YourModel.new.bulk_loader.name

If you set this option to false, +BulkLoader::UnloadAccessError+ occured when you does not call +YourModel.bulk_loader.load explicitly on :name method.

class YourModel
  include BulkLoader::DSL

  bulk_loader :name, :mapped_key, default: nil, autoload: false do |mapped_keys|
    # something with mapped_keys
  end
end

  YourModel.new.name #=> raise error BulkLoader::UnloadAccessError

You can pass this by calling load explicitly.

  model = YourModel.new
  YourModel.bulk_loader.load(:name, [model])
  model.name #=> it does not raise BulkLoader::UnloadAccessError

Add this line to your application's Gemfile:

gem 'bulk_loader'

And then execute:

$ bundle

Or install it yourself as:

$ gem install bulk_loader

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec 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 rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/walf443/bulk_loader.