From 97119f2ba5aed9711465cb408e928190f1c938c7 Mon Sep 17 00:00:00 2001
From: Oliver Severin Mulelid-Tynes <oliver@omt.tech>
Date: Wed, 3 Dec 2025 15:45:45 +0100
Subject: [PATCH] test: add failing test for expr(has_one.function_calc) nil
 poisoning in batch

---
 test/calculation_test.exs         | 44 +++++++++++++++++++++++++++++++
 test/support/resources/chat.ex    |  8 ++++++
 test/support/resources/message.ex | 10 +++++++
 3 files changed, 62 insertions(+)

diff --git a/test/calculation_test.exs b/test/calculation_test.exs
index 4260976c..c38e1847 100644
--- a/test/calculation_test.exs
+++ b/test/calculation_test.exs
@@ -1603,4 +1603,48 @@ defmodule AshPostgres.CalculationTest do
     assert loaded3.active_item_name == nil
     assert loaded3.all_item_name == nil
   end
+
+  test "expr(has_one.function_based_calculation) in batch with nil relationships" do
+    alias AshPostgres.Test.{Chat, Message}
+
+    chat1 = Ash.Seed.seed!(Chat, %{name: "Chat 1"})
+
+    chat2 = Ash.Seed.seed!(Chat, %{name: "Chat 2"})
+
+    Ash.Seed.seed!(Message, %{
+      chat_id: chat2.id,
+      content: "Unread message",
+      read_at: nil
+    })
+
+    chat3 = Ash.Seed.seed!(Chat, %{name: "Chat 3"})
+
+    Ash.Seed.seed!(Message, %{
+      chat_id: chat3.id,
+      content: "Read message",
+      read_at: DateTime.utc_now()
+    })
+
+    single =
+      Chat
+      |> Ash.Query.filter(id == ^chat2.id)
+      |> Ash.Query.load([:last_unread_message_formatted_fn])
+      |> Ash.read!()
+      |> hd()
+
+    assert single.last_unread_message_formatted_fn == "FnMessage: Unread message"
+
+    chats =
+      Chat
+      |> Ash.Query.filter(id in [^chat1.id, ^chat2.id, ^chat3.id])
+      |> Ash.Query.sort(:name)
+      |> Ash.Query.load([:last_unread_message_formatted_fn])
+      |> Ash.read!()
+
+    [loaded1, loaded2, loaded3] = chats
+
+    assert loaded1.last_unread_message_formatted_fn == nil
+    assert loaded2.last_unread_message_formatted_fn == "FnMessage: Unread message"
+    assert loaded3.last_unread_message_formatted_fn == nil
+  end
 end
diff --git a/test/support/resources/chat.ex b/test/support/resources/chat.ex
index 4a819f19..1f0954ac 100644
--- a/test/support/resources/chat.ex
+++ b/test/support/resources/chat.ex
@@ -23,6 +23,14 @@ defmodule AshPostgres.Test.Chat do
     attribute(:name, :string, public?: true)
   end
 
+  calculations do
+    calculate(
+      :last_unread_message_formatted_fn,
+      :string,
+      expr(last_unread_message.formatted_content_fn)
+    )
+  end
+
   relationships do
     belongs_to :last_read_message, AshPostgres.Test.Message do
       allow_nil?(true)
diff --git a/test/support/resources/message.ex b/test/support/resources/message.ex
index 1085c337..20aff86b 100644
--- a/test/support/resources/message.ex
+++ b/test/support/resources/message.ex
@@ -25,6 +25,16 @@ defmodule AshPostgres.Test.Message do
     attribute(:read_at, :utc_datetime, public?: true)
   end
 
+  calculations do
+    calculate :formatted_content_fn, :string do
+      load([:content])
+
+      calculation(fn records, _context ->
+        Enum.map(records, &"FnMessage: #{&1.content}")
+      end)
+    end
+  end
+
   relationships do
     belongs_to :chat, AshPostgres.Test.Chat do
       public?(true)