fix: produce correct error on restrict managed_relationship behavior (#690)

Author: lincolnhuls

lib/data_layer.ex

@@ -2668,7 +2668,15 @@ defmodule AshPostgres.DataLayer do
        ) do
     case Ecto.Adapters.Postgres.Connection.to_constraints(error, []) do
       [] ->
-        {:error, Ash.Error.to_ash_error(error, stacktrace)}
+        constraints = maybe_foreign_key_violation_constraints(error)
+        if constraints != [] do
+          {:error,
+           changeset
+           |> constraints_to_errors(:delete, constraints, resource, error)
+           |> Ash.Error.to_ash_error()}
+        else
+          {:error, Ash.Error.to_ash_error(error, stacktrace)}
+        end
 
       constraints ->
         {:error,
@@ -2682,6 +2690,20 @@ defmodule AshPostgres.DataLayer do
     {:error, Ash.Error.to_ash_error(error, stacktrace)}
   end
 
+  defp maybe_foreign_key_violation_constraints(%Postgrex.Error{postgres: postgres})
+       when is_map(postgres) do
+    code = postgres[:code] || postgres["code"]
+    constraint = postgres[:constraint] || postgres["constraint"]
+
+    if code in ["23503", 23503, :foreign_key_violation] and is_binary(constraint) do
+      [{:foreign_key, constraint}]
+    else
+      []
+    end
+  end
+
+  defp maybe_foreign_key_violation_constraints(_), do: []
+
   defp constraints_to_errors(
          %{constraints: user_constraints} = changeset,
          action,

test/destroy_test.exs

@@ -4,7 +4,30 @@
 
 defmodule AshPostgres.DestroyTest do
   use AshPostgres.RepoCase, async: false
-  alias AshPostgres.Test.Post
+  alias AshPostgres.Test.{Post, Permalink}
+
+  test "destroy with restrict on_delete returns would leave records behind error" do
+    post =
+      Post
+      |> Ash.Changeset.for_create(:create, %{})
+      |> Ash.create!()
+
+    Permalink |> Ash.Changeset.for_create(:create, %{post_id: post.id}) |> Ash.create!()
+
+    assert {:error, %Ash.Error.Invalid{errors: errors}} =
+             post
+             |> Ash.Changeset.for_destroy(:destroy, %{})
+             |> Ash.destroy()
+
+    assert Enum.any?(errors, fn
+             %Ash.Error.Changes.InvalidAttribute{message: msg} ->
+               msg =~ "would leave records behind"
+
+             _ ->
+               false
+           end),
+           "Expected 'would leave records behind' error, got: #{inspect(errors)}"
+  end
 
   test "destroy action destroys the record" do
     post =