feat: add node query

Allow retrieving a resource implementing the Node interface given its Relay
global id.

Close #99

lib/ash_graphql.ex

@@ -137,14 +137,25 @@ defmodule AshGraphql do
             api = unquote(api)
             action_middleware = unquote(action_middleware)
 
-            blueprint_with_queries =
-              api
-              |> AshGraphql.Api.queries(
+            api_queries =
+              AshGraphql.Api.queries(
+                api,
                 unquote(resources),
                 action_middleware,
                 __MODULE__,
                 unquote(relay_ids?)
               )
+
+            relay_queries =
+              if unquote(first?) and unquote(define_relay_types?) and unquote(relay_ids?) do
+                apis_with_resources = unquote(Enum.map(apis, &{elem(&1, 0), elem(&1, 1)}))
+                AshGraphql.relay_queries(apis_with_resources, unquote(schema), __ENV__)
+              else
+                []
+              end
+
+            blueprint_with_queries =
+              (relay_queries ++ api_queries)
               |> Enum.reduce(blueprint, fn query, blueprint ->
                 Absinthe.Blueprint.add_field(blueprint, "RootQueryType", query)
               end)
@@ -351,6 +362,50 @@ defmodule AshGraphql do
     end
   end
 
+  def relay_queries(apis_with_resources, schema, env) do
+    type_to_api_and_resource_map =
+      apis_with_resources
+      |> Enum.flat_map(fn {api, resources} ->
+        resources
+        |> Enum.flat_map(fn resource ->
+          type = AshGraphql.Resource.Info.type(resource)
+
+          if type do
+            [{type, {api, resource}}]
+          else
+            []
+          end
+        end)
+      end)
+      |> Enum.into(%{})
+
+    [
+      %Absinthe.Blueprint.Schema.FieldDefinition{
+        name: "node",
+        identifier: :node,
+        arguments: [
+          %Absinthe.Blueprint.Schema.InputValueDefinition{
+            name: "id",
+            identifier: :id,
+            type: %Absinthe.Blueprint.TypeReference.NonNull{
+              of_type: :id
+            },
+            description: "The Node unique identifier",
+            __reference__: AshGraphql.Resource.ref(env)
+          }
+        ],
+        middleware: [
+          {{AshGraphql.Graphql.Resolver, :resolve_node}, type_to_api_and_resource_map}
+        ],
+        complexity: {AshGraphql.Graphql.Resolver, :query_complexity},
+        module: schema,
+        description: "Retrieves a Node from its global id",
+        type: %Absinthe.Blueprint.TypeReference.NonNull{of_type: :node},
+        __reference__: AshGraphql.Resource.ref(__ENV__)
+      }
+    ]
+  end
+
   defp nested_attrs({:array, type}, constraints, already_checked) do
     nested_attrs(type, constraints[:items] || [], already_checked)
   end

lib/graphql/resolver.ex

@@ -2586,6 +2586,22 @@ defmodule AshGraphql.Graphql.Resolver do
     child_complexity + 1
   end
 
+  def resolve_node(%{arguments: %{id: id}} = resolution, type_to_api_and_resource_map) do
+    case AshGraphql.Resource.decode_relay_id(id) do
+      {:ok, {type, primary_key}} ->
+        {api, resource} = Map.fetch!(type_to_api_and_resource_map, type)
+        # We can be sure this returns something since we check this at compile time
+        query = AshGraphql.Resource.primary_key_get_query(resource)
+
+        # We pass relay_ids? as false since we pass the already decoded primary key
+        put_in(resolution.arguments.id, primary_key)
+        |> resolve({api, resource, query, false})
+
+      {:error, _reason} = error ->
+        Absinthe.Resolution.put_result(resolution, error)
+    end
+  end
+
   def resolve_node_type(%resource{}, _) do
     AshGraphql.Resource.Info.type(resource)
   end

test/relay_ids_test.exs

@@ -1,7 +1,7 @@
 defmodule AshGraphql.RelayIdsTest do
   use ExUnit.Case, async: false
 
-  alias AshGraphql.Test.RelayIds.{Api, Post, Schema, User}
+  alias AshGraphql.Test.RelayIds.{Api, Post, ResourceWithNoPrimaryKeyGet, Schema, User}
 
   setup do
     on_exit(fn ->
@@ -108,4 +108,121 @@ defmodule AshGraphql.RelayIdsTest do
       assert [%{code: "invalid_primary_key"}] = result[:errors]
     end
   end
+
+  describe "node interface and query" do
+    test "allows retrieving resources" do
+      user =
+        User
+        |> Ash.Changeset.for_create(:create, %{name: "fred"})
+        |> Api.create!()
+
+      post =
+        Post
+        |> Ash.Changeset.for_create(
+          :create,
+          %{
+            author_id: user.id,
+            text: "foo",
+            published: true
+          }
+        )
+        |> Api.create!()
+
+      user_relay_id = AshGraphql.Resource.encode_relay_id(user)
+      post_relay_id = AshGraphql.Resource.encode_relay_id(post)
+
+      document =
+        """
+          query Node($id: ID!) {
+          node(id: $id) {
+            __typename
+
+            ... on User {
+              name
+            }
+
+            ... on Post {
+              text
+            }
+          }
+        }
+        """
+
+      resp =
+        document
+        |> Absinthe.run(Schema,
+          variables: %{
+            "id" => post_relay_id
+          }
+        )
+
+      assert {:ok, result} = resp
+
+      refute Map.has_key?(result, :errors)
+
+      assert %{
+               data: %{
+                 "node" => %{
+                   "__typename" => "Post",
+                   "text" => "foo"
+                 }
+               }
+             } = result
+
+      resp =
+        document
+        |> Absinthe.run(Schema,
+          variables: %{
+            "id" => user_relay_id
+          }
+        )
+
+      assert {:ok, result} = resp
+
+      refute Map.has_key?(result, :errors)
+
+      assert %{
+               data: %{
+                 "node" => %{
+                   "__typename" => "User",
+                   "name" => "fred"
+                 }
+               }
+             } = result
+    end
+
+    test "return an error for resources without a primary key get" do
+      resource =
+        ResourceWithNoPrimaryKeyGet
+        |> Ash.Changeset.for_create(:create, %{name: "foo"})
+        |> Api.create!()
+
+      document =
+        """
+          query Node($id: ID!) {
+          node(id: $id) {
+            __typename
+
+            ... on ResourceWithNoPrimaryKeyGet{
+              name
+            }
+          }
+        }
+        """
+
+      resource_relay_id = AshGraphql.Resource.encode_relay_id(resource)
+
+      resp =
+        document
+        |> Absinthe.run(Schema,
+          variables: %{
+            "id" => resource_relay_id
+          }
+        )
+
+      assert {:ok, result} = resp
+
+      assert result[:errors] != nil
+    end
+  end
 end

test/support/relay_ids/registry.ex

@@ -4,6 +4,7 @@ defmodule AshGraphql.Test.RelayIds.Registry do
 
   entries do
     entry(AshGraphql.Test.RelayIds.Post)
+    entry(AshGraphql.Test.RelayIds.ResourceWithNoPrimaryKeyGet)
     entry(AshGraphql.Test.RelayIds.User)
   end
 end

test/support/relay_ids/resources/resource_with_no_primary_key_get.ex

@@ -0,0 +1,38 @@
+defmodule AshGraphql.Test.RelayIds.ResourceWithNoPrimaryKeyGet do
+  @moduledoc false
+
+  use Ash.Resource,
+    data_layer: Ash.DataLayer.Ets,
+    extensions: [AshGraphql.Resource]
+
+  graphql do
+    type :resource_with_no_primary_key_get
+
+    queries do
+      get :get_resource_by_name, :get_by_name
+    end
+
+    mutations do
+      create :create_resource, :create
+    end
+  end
+
+  actions do
+    defaults([:create, :update, :destroy, :read])
+
+    read(:get_by_name, get_by: :name)
+  end
+
+  attributes do
+    uuid_primary_key(:id)
+    attribute(:name, :string, allow_nil?: false)
+  end
+
+  identities do
+    identity(:name, [:name], pre_check_with: AshGraphql.Test.RelayIds.Api)
+  end
+
+  relationships do
+    has_many(:posts, AshGraphql.Test.RelayIds.Post, destination_attribute: :author_id)
+  end
+end

test/support/relay_ids/resources/user.ex

@@ -8,6 +8,10 @@ defmodule AshGraphql.Test.RelayIds.User do
   graphql do
     type :user
 
+    queries do
+      get :get_user, :read
+    end
+
     mutations do
       create :create_user, :create
     end