Handle composite foreign keys in positioning scope changes

lib/positioning/mechanisms.rb

@@ -215,7 +215,7 @@ def in_positioning_scope?
     end
 
     def positioning_scope_changed?
-      scope_columns.any? do |scope_column|
+      scope_columns.flatten.any? do |scope_column|
         @positioned.attribute_changed?(scope_column)
       end
     end

test/models/composite_foreign_key_item.rb

@@ -0,0 +1,5 @@
+class CompositeForeignKeyItem < ActiveRecord::Base
+  belongs_to :list, class_name: "CompositePrimaryKeyItem", foreign_key: [:cpki_item_id, :cpki_account_id]
+
+  positioned on: :list
+end

test/models/composite_primary_key_item.rb

@@ -3,5 +3,7 @@ class CompositePrimaryKeyItem < ActiveRecord::Base
 
   belongs_to :list
 
+  has_many :composite_foreign_key_items, -> { order(:position) }, foreign_key: [:cpki_item_id, :cpki_account_id], dependent: :destroy
+
   positioned on: :list
 end

test/support/active_record.rb

@@ -55,6 +55,15 @@
 
     add_index :composite_primary_key_items, [:list_id, :position], unique: true
 
+    create_table :composite_foreign_key_items, force: true do |t|
+      t.string :name
+      t.integer :position, null: false
+      t.integer :cpki_item_id, null: false
+      t.integer :cpki_account_id, null: false
+    end
+
+    add_index :composite_foreign_key_items, [:cpki_item_id, :cpki_account_id, :position], unique: true, name: "index_cfki_on_scope_and_position"
+
     create_table :categories, force: true do |t|
       t.string :name
       t.integer :position, null: false

test/test_helper.rb

@@ -11,6 +11,7 @@
 require_relative "models/new_item"
 require_relative "models/default_scope_item"
 require_relative "models/composite_primary_key_item"
+require_relative "models/composite_foreign_key_item"
 require_relative "models/product"
 require_relative "models/category"
 require_relative "models/categorised_item"

test/test_positioning.rb

@@ -566,6 +566,19 @@ 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")
+    parent = CompositePrimaryKeyItem.create(item_id: 1, account_id: 1, list: list, name: "Parent")
+    child = parent.composite_foreign_key_items.create(name: "Child 1")
+    parent.composite_foreign_key_items.create(name: "Child 2")
+
+    mechanisms = Positioning::Mechanisms.new(child, :position)
+    refute mechanisms.send(:destroyed_via_positioning_scope?)
+
+    parent.destroy
+    assert mechanisms.send(:destroyed_via_positioning_scope?)
+  end
 end
 
 class TestPositioningScopes < Minitest::Test
@@ -606,6 +619,13 @@ def test_that_position_columns_will_cope_with_polymorphic_belong_to
     assert_equal({position: {scope_columns: ["includable_id", "includable_type"], scope_associations: [:includable]}}, Entity.positioning_columns)
   end
 
+  def test_that_position_columns_will_cope_with_composite_foreign_key
+    assert_equal(
+      {position: {scope_columns: [["cpki_item_id", "cpki_account_id"]], scope_associations: [:list]}},
+      CompositeForeignKeyItem.positioning_columns
+    )
+  end
+
   def test_that_position_columns_must_have_unique_keys
     assert_raises(Positioning::Error) do
       Item.send :positioned, on: :list
@@ -1135,8 +1155,6 @@ def test_destroying_multiple_items
 
 class TestCompositePrimaryKeyPositioning < TestPositioning
   def configure
-    skip if ActiveRecord.version < Gem::Version.new("7.1.0")
-
     @association = :composite_primary_key_items
     @id = Enumerator.new do |yielder|
       number = 1
@@ -1149,6 +1167,38 @@ def configure
   end
 end
 
+class TestCompositeForeignKeyPositioning < TestPositioning
+  def configure
+    @association = :composite_foreign_key_items
+    @id = Enumerator.new do |yielder|
+      loop do
+        yielder.yield(nil)
+      end
+    end
+  end
+
+  def setup
+    configure
+
+    list = List.create name: "List"
+    @first_list = CompositePrimaryKeyItem.create(item_id: 1, account_id: 1, list: list, name: "First List")
+    @second_list = CompositePrimaryKeyItem.create(item_id: 2, account_id: 2, list: list, name: "Second List")
+    @first_item = @first_list.send(@association).create id: @id.next, name: "First Item"
+    @second_item = @first_list.send(@association).create id: @id.next, name: "Second Item"
+    @third_item = @first_list.send(@association).create id: @id.next, name: "Third Item"
+    @fourth_item = @second_list.send(@association).create id: @id.next, name: "Fourth Item"
+    @fifth_item = @second_list.send(@association).create id: @id.next, name: "Fifth Item"
+    @sixth_item = @second_list.send(@association).create id: @id.next, name: "Sixth Item"
+
+    @models = [
+      @first_list, @second_list, @first_item, @second_item,
+      @third_item, @fourth_item, @fifth_item, @sixth_item
+    ]
+
+    reload_models
+  end
+end
+
 class TestNoScopePositioning < Minitest::Test
   include Minitest::Hooks