Handle composite foreign keys in positioning scope changes

lib/positioning.rb

@@ -35,7 +35,7 @@ def positioned(on: [], column: :position)
             reflection = reflections[scope_component]
 
             if reflection&.belongs_to?
-              positioning_columns[column][:scope_columns] << reflection.foreign_key
+              positioning_columns[column][:scope_columns].concat Array(reflection.foreign_key).map(&:to_s)
               positioning_columns[column][:scope_columns] << reflection.foreign_type if reflection.polymorphic?
               positioning_columns[column][:scope_associations] << reflection.name
             else

lib/positioning/mechanisms.rb

@@ -221,8 +221,12 @@ def positioning_scope_changed?
     end
 
     def destroyed_via_positioning_scope?
-      @positioned.destroyed_by_association && scope_columns.any? do |scope_column|
-        @positioned.destroyed_by_association.foreign_key == scope_column
+      return false unless @positioned.destroyed_by_association
+
+      foreign_keys = Array(@positioned.destroyed_by_association.foreign_key).map(&:to_s)
+
+      scope_columns.any? do |scope_column|
+        foreign_keys.include?(scope_column.to_s)
       end
     end
   end

test/test_positioning.rb

@@ -566,6 +566,32 @@ def test_destroyed_via_positioning_scope?
     list.destroy
     assert mechanisms.send(:destroyed_via_positioning_scope?)
   end
+
+  def test_destroyed_via_positioning_scope_with_composite_foreign_key
+    list = List.create name: "List"
+    item = list.items.create name: "Item"
+
+    mechanisms = Positioning::Mechanisms.new(item, :position)
+
+    mock_association = mock
+    mock_association.stubs(:foreign_key).returns(["list_id", "other_key"])
+    item.stubs(:destroyed_by_association).returns(mock_association)
+
+    assert mechanisms.send(:destroyed_via_positioning_scope?)
+  end
+
+  def test_destroyed_via_positioning_scope_with_composite_foreign_key_no_match
+    list = List.create name: "List"
+    item = list.items.create name: "Item"
+
+    mechanisms = Positioning::Mechanisms.new(item, :position)
+
+    mock_association = mock
+    mock_association.stubs(:foreign_key).returns(["other_key", "another_key"])
+    item.stubs(:destroyed_by_association).returns(mock_association)
+
+    refute mechanisms.send(:destroyed_via_positioning_scope?)
+  end
 end
 
 class TestPositioningScopes < Minitest::Test