A Yaks policy to work on Sequel::Dataset (without converting them to Array first)

collection_mapper.rb

module YaksSequel
  class CollectionMapper < Yaks::CollectionMapper
    attr_reader :collection_dataset

    def call(collection, *args)
      return super unless collection.is_a?(Sequel::Dataset)

      @collection_dataset = collection
      if collection.opts[:eager_graph]
        super(collection.all, *args)
      else
        super
      end
    end
  end
end

paginated_collection_mapper.rb

module YaksSequel
  # Pagination Mapper for Sequel's pagination extension.
  #
  # This mapper works on a `Sequel::Dataset::Pagination`. It does not paginate
  # by itself.
  #
  # It will create links using the `page[number]` and `page[size]` request query
  # parameters.
  class PaginatedCollectionMapper < YaksSequel::CollectionMapper
    include Memoizable

    PAGE_NUMBER_PARAM = "page%5Bnumber%5D"
    PAGE_SIZE_PARAM   = "page%5Bsize%5D"

    link :first, -> { link_to_page(1) }
    link :prev,  -> { link_to_page(collection_dataset.prev_page) }
    link :next,  -> { link_to_page(collection_dataset.next_page) }
    link :last,  -> { link_to_page(collection_dataset.page_count) }

    def params
      Rack::Request.new(env).params
    end
    memoize :params

    def requested_page_size
      params.dig("page", "size").to_i.nonzero?
    end
    memoize :requested_page_size

    def paged_link_template
      URITemplate.new("#{env['PATH_INFO']}{?#{PAGE_SIZE_PARAM},#{PAGE_NUMBER_PARAM}}")
    end
    memoize :paged_link_template

    def link_to_page(page_num)
      paged_link_template.expand(PAGE_NUMBER_PARAM => page_num, PAGE_SIZE_PARAM => requested_page_size) if page_num
    end
  end
end

policy.rb

module YaksSequel
  class Policy < Yaks::DefaultPolicy
    def derive_mapper_from_object(model)
      return super unless model.is_a?(Sequel::Dataset)
      derive_mapper_from_collection(model)
    end

    def derive_type_from_collection(collection)
      return super unless collection.is_a?(Sequel::Dataset)
      underscore(collection.model.name.split("::").last.sub(/Mapper$/, ""))
    end

    def derive_mapper_from_collection(collection)
      return super unless collection.is_a?(Sequel::Dataset)

      model_name = collection.model.name.split("::").last

      if collection.is_a?(Sequel::Dataset::Pagination)
        name = "#{model_name}PaginatedCollectionMapper"
        begin
          return @options[:namespace].const_get(name)
        rescue NameError
        end

        PaginatedCollectionMapper
      else
        name = "#{model_name}CollectionMapper"
        begin
          return @options[:namespace].const_get(name)
        rescue NameError
        end

        CollectionMapper
      end
    end
  end
end