Add dataloader support for resolving N+1 queries

lib/crudimentary/absinthe/dataloader/source.ex

@@ -0,0 +1,11 @@
+defmodule CertifyEdWeb.API.Graphql.Dataloader.Source do
+  import Ecto.Query
+
+  @repo Confex.get_env(CRUDimentary.MixProject.project()[:app], :repo)
+
+  def data(), do: Dataloader.Ecto.new(@repo, query: &query/2)
+
+  defp query(queryable, _params) do
+    from(q in queryable, select: %{data: q})
+  end
+end

lib/crudimentary/absinthe/middlewares/default.ex

@@ -1,17 +1,19 @@
 defmodule CRUDimentary.Absinthe.Middlewares.Default do
   def call(%{source: source} = resolution, %{field: field, object: object}) do
-    value =
-      with %_{} <- source,
-           false <- String.ends_with?(object.name, "Result"),
-           object_resolver when not is_nil(object_resolver) <- extract_object_resolver(object),
-           {:ok, value} <-
-             object_resolver.(source, resolution.definition.argument_data, resolution) do
-        value
-      else
-        _ -> Map.get(source, field.identifier)
-      end
+    with %_{} <- source,
+         false <- String.ends_with?(object.name, "Result"),
+         object_resolver when not is_nil(object_resolver) <- extract_object_resolver(object) do
+      case object_resolver.(source, resolution.definition.argument_data, resolution) do
+        {:ok, value} ->
+          add_resolution_value(resolution, value)
 
-    %{resolution | state: :resolved, value: value}
+        {:middleware, module, opts} ->
+          add_resolution_middlware(resolution, {module, opts})
+      end
+    else
+      _ ->
+        add_resolution_value(resolution, Map.get(source, field.identifier))
+    end
   end
 
   defp extract_object_resolver(object) do
@@ -23,4 +25,12 @@ defmodule CRUDimentary.Absinthe.Middlewares.Default do
       nil
     end
   end
+
+  defp add_resolution_value(resolution, value) do
+    %{resolution | state: :resolved, value: value}
+  end
+
+  defp add_resolution_middlware(resolution, middleware) do
+    %{resolution | state: :unresolved, middleware: [middleware | resolution.middleware]}
+  end
 end

mix.exs

@@ -31,7 +31,8 @@ defmodule CRUDimentary.MixProject do
       {:odgn_json_pointer, "~> 2.3"},
       {:paginator, "~> 0.3"},
       {:phoenix, ">= 0.0.0"},
-      {:confex, "~> 3.3.1"}
+      {:confex, "~> 3.3.1"},
+      {:dataloader, "~> 1.0.4"}
     ]
   end
 end

mix.lock

@@ -3,6 +3,7 @@
   "absinthe_plug": {:hex, :absinthe_plug, "1.4.5", "f63d52a76c870cd5f11d4bed8f61351ab5c5f572c5eb0479a0137f9f730ba33d", [:mix], [{:absinthe, "~> 1.4.11", [hex: :absinthe, repo: "hexpm", optional: false]}, {:plug, "~> 1.3.2 or ~> 1.4", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm"},
   "base64url": {:hex, :base64url, "0.0.1", "36a90125f5948e3afd7be97662a1504b934dd5dac78451ca6e9abf85a10286be", [:rebar], [], "hexpm"},
   "confex": {:hex, :confex, "3.3.1", "8febaf751bf293a16a1ed2cbd258459cdcc7ca53cfa61d3f83d49dd276a992b4", [:mix], [], "hexpm"},
+  "dataloader": {:hex, :dataloader, "1.0.4", "7c2345c53c9e5b61420013fc53c8463ba347a938b61f66677eb47d9c4a53ac5d", [:mix], [{:ecto, ">= 0.0.0", [hex: :ecto, repo: "hexpm", optional: true]}], "hexpm"},
   "decimal": {:hex, :decimal, "1.5.0", "b0433a36d0e2430e3d50291b1c65f53c37d56f83665b43d79963684865beab68", [:mix], [], "hexpm"},
   "delirium_tremex": {:git, "https://github.com/floatingpointio/delirium_tremex.git", "b1c487386f9b822cf9a398620a1d355b86b3b867", []},
   "earmark": {:hex, :earmark, "1.2.5", "4d21980d5d2862a2e13ec3c49ad9ad783ffc7ca5769cf6ff891a4553fbaae761", [:mix], [], "hexpm"},