schema.ex

defmodule Bling.GraphQL.Schema do
  use Absinthe.Schema

  def middleware([]=middleware, _field, _object), do: middleware

  def middleware(middleware, field, object) do
    Bling.GraphQL.ScoutMiddleware.instrument(middleware, field, object)
  end
  query do
   #...
   end
end
   

scout_apm_middleware.ex

defmodule Bling.GraphQL.ScoutMiddleware do
  @behaviour Absinthe.Middleware
  @behaviour Absinthe.Plugin

  def call( res, {:start,  object_identifier, field_identifier }) do
    IO.puts "Scout middleware"
    ScoutApm.TrackedRequest.start_layer("Controller", "#{object_identifier}/#{field_identifier}" )
    res
  end

  # def after_resolution(acc=%{__MODULE__: [layer_on | layers_after]}) do
  def call( res, {:end,  object_identifier, field_identifier }) do
    ScoutApm.TrackedRequest.stop_layer fn
      layer -> layer
    end

    res
  end

  def instrument(middleware, field, object) do
    [{{ __MODULE__,:call}, {:start, object.identifier, field.identifier}  } | middleware ] ++ [{{__MODULE__, :call}, {:end, object.identifier, field.identifier}}]
  end
end