GraphQL-Ruby lookahead to plan sql queries by alias

lookahead_example.rb

require "bundler/inline"

gemfile do
  gem "graphql", "2.3.7"
  gem "sqlite3", "~>1.4"
  gem "activerecord", require: "active_record"
end

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Schema.define do
  self.verbose = false
  create_table :books, force: true do |t|
    t.column :author, :string
    t.column :title, :string
    t.column :stars, :integer
    t.column :library_id, :integer
  end

  create_table :libraries, force: true do |t|
    t.column :name, :string
  end
end

class Library < ActiveRecord::Base; end
l1 = Library.create!(name: "Clemons")
l2 = Library.create!(name: "Alderman")

class Book < ActiveRecord::Base; end

Book.belongs_to(:library)
Library.has_many(:books)

Book.create!(title: "Remembering", author: "Wendell Berry", stars: 3, library: l1)
Book.create!(title: "The Going to Bed Book", author: "Sandra Boynton", stars: 5, library: l1)
Book.create!(title: "Historical Brewing Techniques", author: "Lars Marius Garshol", stars: 4, library: l2)
Book.create!(title: "The Tale of Tom Kitten", author: "Beatrix Potter", stars: 3, library: l2)

class BookSchema < GraphQL::Schema
  class Book < GraphQL::Schema::Object
    field :author, String
    field :title, String
    field :stars, Integer
  end

  class Library < GraphQL::Schema::Object
    field :books, [Book],  extras: [:ast_node]

    def books(ast_node:)
      @object[:books][ast_node.alias]
    end
  end

  class Query < GraphQL::Schema::Object
    field :libraries, [Library], extras: [:lookahead, :ast_node]

    def libraries(lookahead:, ast_node:)
      book_lookahead = lookahead.selection(:books)
      aliases = book_lookahead.ast_nodes.map(&:alias).uniq
      alias_fields = {}

      aliases.each do |b_alias|
        b_alias_fields = lookahead.alias_selection(b_alias).selections.map(&:name)
        alias_fields[b_alias] = b_alias_fields
      end

      ::Library.all.map do |library|
        result = {}
        alias_fields.each do |b_alias, fields|
          result[b_alias] = library.books.select(fields)
        end
        { books: result }
      end
    end
  end

  query(Query)
end

ActiveRecord::Base.logger = Logger.new($stdout)

pp BookSchema.execute("{
  libraries {
    books1: books { title }
    books2: books { author stars }
  }
}").to_h