Association dataloader with graphql-ruby

association.rb

# official docs: https://graphql-ruby.org/dataloader/sources.html

# app/graphql/sources/association.rb
class Sources::Association < ::GraphQL::Dataloader::Source
  def initialize(association_name, scope = nil)
    @association_name = association_name
    @scope = scope
  end

  def fetch(records)
    ::ActiveRecord::Associations::Preloader.new.preload(records, @association_name, @scope)
    # Rails7
    # ::ActiveRecord::Associations::Preloader.new(records: records, associations: @association_name, scope: @scope).call
    records.map { |record| record.public_send(@association_name) }
  end

  # https://github.com/rmosolgo/graphql-ruby/blob/821ca53048fa5803fb90596719b4fedd65029ecb/lib/graphql/dataloader/source.rb#L113-L129
  def self.batch_key_for(*batch_args, **batch_kwargs)
    [*batch_args.map { |arg| arg.try(:to_sql) || arg }, **batch_kwargs]
  end
end

example.rb

class User < ApplicationRecord
  has_many :posts
end
class Post < ApplicationRecord
  belongs_to :user
  has_many :comments
end
class Comment < ApplicationRecord
  belongs_to :post
end

module Types
  class UserType < Types::BaseObject
    field :id, ID, null: false
    field :posts, [Types::PostType], null: false
    def posts
      dataloader.with(Sources::Association, :posts, ::Post.preload(:comments)).load(object)
    end
  end
  
  class PostType < Types::BaseObject
    field :id, ID, null: false
    field :user, Types::UserType, null: false
    def user
      dataloader.with(Sources::Association, :user).load(object)
    end
    field :comments, [Types::CommentType], null: false
    def comments
      dataloader.with(Sources::Association, :comments).load(object)
    end
  end
  
  class CommentType < Types::BaseObject
    field :id, ID, null: false
    field :post, Types::PostType, null: false
    def post
      dataloader.with(Sources::Association, :post).load(object)
    end
  end
end

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