fix: properly load manual to_one relationships

lib/ash/actions/load.ex

@@ -230,7 +230,11 @@ defmodule Ash.Actions.Load do
 
   defp attach_to_one_loads(value, %{name: name, no_attributes?: true}, data, lead_path) do
     map_or_update(data, lead_path, fn record ->
-      Map.put(record, name, value |> List.wrap() |> Enum.at(0))
+      if is_map(data) do
+        Map.put(record, name, value |> List.wrap() |> Enum.at(0) |> elem(1))
+      else
+        Map.put(record, name, value |> List.wrap() |> Enum.at(0))
+      end
     end)
   end
 
@@ -248,7 +252,7 @@ defmodule Ash.Actions.Load do
 
     map_or_update(data, lead_path, fn record ->
       related =
-        Enum.filter(value, fn {key, _value} ->
+        Enum.find_value(value, fn {key, value} ->
           key =
             if is_map(key) || !single_primary_key do
               key
@@ -257,10 +261,16 @@ defmodule Ash.Actions.Load do
             end
 
           if last_relationship.source.primary_key_matches?(record, key) do
-            value
+            {:ok, value}
           end
         end)
-        |> List.wrap()
+        |> case do
+          {:ok, value} ->
+            value
+
+          _ ->
+            nil
+        end
 
       Map.put(
         record,

lib/ash/resource.ex

@@ -122,7 +122,7 @@ defmodule Ash.Resource do
                               |> Enum.filter(& &1.primary_key?)
                               |> Enum.map(&{&1.name, &1.type})
 
-      @primary_key @primary_key_with_types |> Enum.map(&elem(&1, 1))
+      @primary_key @primary_key_with_types |> Enum.map(&elem(&1, 0))
 
       if Ash.Resource.Info.primary_key_simple_equality?(__MODULE__) do
         def primary_key_matches?(left, right) do

test/policy/complex_test.exs

@@ -91,6 +91,14 @@ defmodule Ash.Test.Policy.ComplexTest do
              |> Api.read!(actor: me)
   end
 
+  test "it properly scopes single loads" do
+    assert [%{best_friend: %{name: "me"}}] =
+             User
+             |> Ash.Query.filter(best_friend.name == "me")
+             |> Api.read!()
+             |> Api.load!(:best_friend)
+  end
+
   test "aggregates can be loaded", %{me: me} do
     Post
     |> Ash.Query.load(:count_of_comments)

test/support/policy_complex/resources/user/reationships/best_friend.ex

@@ -0,0 +1,50 @@
+defmodule Ash.Test.Support.PolicyComplex.User.Relationships.BestFriend do
+  @moduledoc false
+  use Ash.Resource.ManualRelationship
+  require Ash.Query
+
+  def load(users, _, %{api: api, query: query}) do
+    user_ids = Enum.map(users, & &1.id)
+
+    friend_links =
+      Ash.Test.Support.PolicyComplex.FriendLink
+      |> Ash.Query.filter(source_id in ^user_ids or destination_id in ^user_ids)
+      |> api.read!()
+
+    all_relevant_user_ids =
+      friend_links
+      |> Enum.flat_map(fn %{source_id: source_id, destination_id: destination_id} ->
+        [source_id, destination_id]
+      end)
+      |> Enum.uniq()
+
+    all_relevant_users =
+      query
+      |> Ash.Query.filter(id in ^all_relevant_user_ids)
+      |> api.read!()
+      |> Map.new(&{&1.id, &1})
+
+    {:ok,
+     Map.new(users, fn user ->
+       best_friend =
+         friend_links
+         |> Enum.filter(fn %{source_id: source_id, destination_id: destination_id} ->
+           source_id == user.id || destination_id == user.id
+         end)
+         |> Enum.flat_map(fn %{source_id: source_id, destination_id: destination_id} ->
+           if source_id == user.id do
+             Map.get(all_relevant_users, destination_id)
+           else
+             Map.get(all_relevant_users, source_id)
+           end
+           |> List.wrap()
+         end)
+         |> Enum.uniq()
+         # obviously a weird heuristic for being someone's best friend 😆
+         |> Enum.sort_by(&String.jaro_distance(user.name, &1.name))
+         |> Enum.at(0)
+
+       {user.id, best_friend}
+     end)}
+  end
+end

test/support/policy_complex/resources/user/user.ex

@@ -69,5 +69,9 @@ defmodule Ash.Test.Support.PolicyComplex.User do
     has_many :friends, Ash.Test.Support.PolicyComplex.User do
       manual Ash.Test.Support.PolicyComplex.User.Relationships.Friends
     end
+
+    has_one :best_friend, Ash.Test.Support.PolicyComplex.User do
+      manual Ash.Test.Support.PolicyComplex.User.Relationships.BestFriend
+    end
   end
 end