test: aggregate with parent ref in relationship filter and sorting on relationship field

test/aggregate_test.exs

@@ -8,6 +8,7 @@
   alias AshPostgres.Test.{Author, Chat, Comment, Organization, Post, Rating, User}
 
   require Ash.Query
+  require Ash.Sort
   import Ash.Expr
 
   test "nested sum aggregates" do
@@ -101,7 +102,7 @@
     assert read_post.count_of_comments == 1
   end
 
   test "nested filters on aggregates works" do
     org =
       Organization
       |> Ash.Changeset.for_create(:create, %{name: "match"})
@@ -1920,6 +1921,81 @@
     end
   end
 
+  test "aggregate with parent() ref in relationship filter and sorting on relationship field" do
+    chat_1 =
+      Chat
+      |> Ash.Changeset.for_create(:create, %{name: "Test Chat"})
+      |> Ash.create!()
+
+    chat_1_message_1 =
+      AshPostgres.Test.Message
+      |> Ash.Changeset.for_create(:create, %{
+        chat_id: chat_1.id,
+        content: "First message",
+        sent_at: DateTime.add(DateTime.utc_now(), -3600, :second)
+      })
+      |> Ash.create!()
+
+    _chat_1_message_2 =
+      AshPostgres.Test.Message
+      |> Ash.Changeset.for_create(:create, %{
+        chat_id: chat_1.id,
+        content: "Second message",
+        sent_at: DateTime.add(DateTime.utc_now(), -1800, :second)
+      })
+      |> Ash.create!()
+
+    # Update chat to set last_read_message to the first message
+    # This means message_2 should be "unread"
+    _chat =
+      chat_1
+      |> Ash.Changeset.for_update(:update, %{last_read_message_id: chat_1_message_1.id})
+      |> Ash.update!()
+
+    # Create a second chat to force multiple records and trigger DISTINCT ON
+    chat_2 =
+      Chat
+      |> Ash.Changeset.for_create(:create, %{name: "Test Chat 2"})
+      |> Ash.create!()
+
+    chat_2_message_1 =
+      AshPostgres.Test.Message
+      |> Ash.Changeset.for_create(:create, %{
+        chat_id: chat_2.id,
+        content: "Chat 2 - Message 1",
+        sent_at: DateTime.add(DateTime.utc_now(), -100, :second)
+      })
+      |> Ash.create!()
+
+    AshPostgres.Test.Message
+    |> Ash.Changeset.for_create(:create, %{
+      chat_id: chat_2.id,
+      content: "Chat 2 - Message 2",
+      sent_at: DateTime.utc_now()
+    })
+    |> Ash.create!()
+
+    chat_2
+    |> Ash.Changeset.for_update(:update, %{last_read_message_id: chat_2_message_1.id})
+    |> Ash.update!()
+
+    # This query exercises the following conditions:
+    # - select() excludes last_read_message_id from the query
+    # - Sorting by last_message.sent_at (has_one from_many?) causes DISTINCT ON + subquery wrapping
+    # - Loading unread_messages_count_alt (aggregate on relationship with parent() in filter)
+    #   uses a lateral join that references parent(last_read_message_id)
+    # - The wrapped subquery must include last_read_message_id for the lateral join to work
+    result =
+      Chat
+      |> Ash.Query.filter(id in [^chat_1.id, ^chat_2.id])
+      |> Ash.Query.select([:id, :name])
+      |> Ash.Query.load(:unread_messages_count_alt)
+      |> Ash.Query.sort([{Ash.Sort.expr_sort(expr(last_message.sent_at)), :asc}])
+      |> Ash.read!()
+
+    assert length(result) == 2
+  end
+
   test "multiple aggregates filtering on nested first aggregate" do
     post =
       Post

test/support/resources/chat.ex

@@ -46,12 +46,22 @@ defmodule AshPostgres.Test.Chat do
       filter(expr(is_nil(read_at)))
       sort(sent_at: :desc)
     end
+
+    has_many :unread_messages, AshPostgres.Test.Message do
+      public?(true)
+      no_attributes?(true)
+      filter(expr(is_nil(parent(last_read_message_id)) or id > parent(last_read_message_id)))
+    end
   end
 
   aggregates do
     count :unread_message_count, :messages do
       public?(true)
       filter(expr(is_nil(parent(last_read_message_id)) or id > parent(last_read_message_id)))
     end
+
+    count :unread_messages_count_alt, :unread_messages do
+      public?(true)
+    end
   end
 end