demonstrate bug with joining across aggregates

priv/resource_snapshots/test_repo/tags/20260105194602.json

@@ -0,0 +1,56 @@
+{
+  "attributes": [
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"gen_random_uuid()\")",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": true,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "id",
+      "type": "uuid"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "title",
+      "type": "text"
+    },
+    {
+      "allow_nil?": false,
+      "default": "0",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "importance",
+      "type": "bigint"
+    }
+  ],
+  "base_filter": null,
+  "check_constraints": [],
+  "create_table_options": null,
+  "custom_indexes": [],
+  "custom_statements": [],
+  "has_create_action": true,
+  "hash": "8357381E60B641F3A2F66AF2B3830CCFADFB6EFC281D65A0AA4BCD714A611B0E",
+  "identities": [],
+  "multitenancy": {
+    "attribute": null,
+    "global": null,
+    "strategy": null
+  },
+  "repo": "Elixir.AshPostgres.TestRepo",
+  "schema": null,
+  "table": "tags"
+}

priv/test_repo/migrations/20260105194602_add_title_to_tags.exs

@@ -0,0 +1,21 @@
+defmodule AshPostgres.TestRepo.Migrations.AddTitleToTags do
+  @moduledoc """
+  Updates resources based on their most recent snapshots.
+
+  This file was autogenerated with `mix ash_postgres.generate_migrations`
+  """
+
+  use Ecto.Migration
+
+  def up do
+    alter table(:tags) do
+      add(:title, :text)
+    end
+  end
+
+  def down do
+    alter table(:tags) do
+      remove(:title)
+    end
+  end
+end

test/aggregate_test.exs

@@ -738,6 +738,31 @@
 
       assert Enum.sort(user.years_visited) == ["1955", "1985", "1985", "2015"]
     end
+
+    test "reproduction of a bug where joins involving an aggregate use the wrong id on a join condition" do
+      tag =
+        AshPostgres.Test.Tag
+        |> Ash.Changeset.for_create(:create, %{title: "Hello There"})
+        |> Ash.create!()
+
+      post =
+        AshPostgres.Test.Post
+        |> Ash.Changeset.for_create(:create, %{title: "A Post"})
+        |> Ash.create!()
+
+      comment =
+        AshPostgres.Test.Comment
+        |> Ash.Changeset.for_create(:create, %{title: "Hello There"})
+        |> Ash.Changeset.manage_relationship(:post, post, type: :append_and_remove)
+        |> Ash.create!()
+
+      _post_tag =
+        AshPostgres.Test.PostTag
+        |> Ash.Changeset.for_create(:create, %{post_id: post.id, tag_id: tag.id})
+        |> Ash.create!()
+
+      assert Ash.calculate!(tag, :has_post_with_comment_with_same_title) == true
+    end
   end
 
   describe "first" do

test/support/resources/tag.ex

@@ -25,6 +25,7 @@ defmodule AshPostgres.Test.Tag do
 
   attributes do
     uuid_primary_key(:id)
+    attribute(:title, :string, allow_nil?: true, public?: true)
     attribute(:importance, :integer, allow_nil?: false, default: 0, public?: true)
   end
 
@@ -48,4 +49,12 @@ defmodule AshPostgres.Test.Tag do
       sort(score_after_winning: :desc)
     end
   end
+
+  calculations do
+    calculate(
+      :has_post_with_comment_with_same_title,
+      :boolean,
+      expr(title in posts.uniq_comment_titles)
+    )
+  end
 end