Avoiding N+1 loads in different GraphQL subtrees

list_of_nodes_example.rb

require "bundler/inline"

gemfile do
  gem "graphql", "2.5.0"
  gem "activerecord", require: "active_record"
  gem "sqlite3"
  gem "logger"
end

# Set up the database for the example
ActiveRecord::Base.establish_connection({ adapter: "sqlite3", database: ":memory:" })
ActiveRecord::Schema.define do
  self.verbose = false
  create_table :books do |t|
    t.string :title
    t.integer :author_id
  end

  create_table :authors do |t|
    t.string :name
  end
end

class Author < ActiveRecord::Base
  has_many :books
end

class Book < ActiveRecord::Base
  belongs_to :author
end

a1 = Author.create(name: "Beatrix Potter")
a1.books.create!(title: "The Tale of Ginger and Pickles")
a1.books.create!(title: "The Tale of Samuel Whiskers")

a2 = Author.create!(name: "Sandra Boynton")
a2.books.create!(title: "Birthday Monsters")
a2.books.create!(title: "But Not the Hippopotamus")

class MySchema < GraphQL::Schema
  class Author < GraphQL::Schema::Object
    field :name, String
  end

  class Book < GraphQL::Schema::Object
    field :title, String
    field :author, Author

    if ENV["WITH_DATALOADER"]
      def author
        # Could also be:
        #   dataloader.with(GraphQL::Dataloader::ActiveRecordAssociationSource, :author).load(object)
        dataload_association(:author)
      end
    end
  end

  class Query < GraphQL::Schema::Object
    field :books, [Book] do
      argument :ids, [ID]
    end

    def books(ids:)
      ::Book.where(id: ids)
    end
  end

  query(Query)
  use GraphQL::Dataloader
end

ActiveRecord::Base.logger = Logger.new(STDOUT)
pp MySchema.execute <<~GRAPHQL
query GetManyBooks {
  books(ids: [1, 2, 3, 4]) {
    title
    author {
     name
    }
  }
}
GRAPHQL

# ruby list_of_nodes_example.rb
# D, [2025-04-01T18:22:15.672155 #86219] DEBUG -- :   Book Load (0.1ms)  SELECT "books".* FROM "books" WHERE "books"."id" IN (?, ?, ?, ?)  [["id", 1], ["id", 2], ["id", 3], ["id", 4]]
# D, [2025-04-01T18:22:15.673230 #86219] DEBUG -- :   Author Load (0.1ms)  SELECT "authors".* FROM "authors" WHERE "authors"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]
# D, [2025-04-01T18:22:15.673620 #86219] DEBUG -- :   Author Load (0.0ms)  SELECT "authors".* FROM "authors" WHERE "authors"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]
# D, [2025-04-01T18:22:15.673945 #86219] DEBUG -- :   Author Load (0.0ms)  SELECT "authors".* FROM "authors" WHERE "authors"."id" = ? LIMIT ?  [["id", 2], ["LIMIT", 1]]
# D, [2025-04-01T18:22:15.674262 #86219] DEBUG -- :   Author Load (0.0ms)  SELECT "authors".* FROM "authors" WHERE "authors"."id" = ? LIMIT ?  [["id", 2], ["LIMIT", 1]]
# 
# WITH_DATALOADER=1 ruby list_of_nodes_example.rb
# D, [2025-04-01T18:22:23.088179 #86235] DEBUG -- :   Book Load (0.2ms)  SELECT "books".* FROM "books" WHERE "books"."id" IN (?, ?, ?, ?)  [["id", 1], ["id", 2], ["id", 3], ["id", 4]]
# D, [2025-04-01T18:22:23.095555 #86235] DEBUG -- :   Author Load (0.2ms)  SELECT "authors".* FROM "authors" WHERE "authors"."id" IN (?, ?)  [["id", 1], ["id", 2]]