Version 0.4.3 - Add support for polymorphic belongs_to

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## [Unreleased]
 
+## [0.4.3] - 2024-11-18
+
+- Add support for polymorphic `belongs_to` where we add both the `id` and the `type` to the scope.
+
 ## [0.4.2] - 2024-11-08
 
 NOTE: Versions 0.4.0 and 0.4.1 contain fatal flaws with the locking logic. Upgrade as soon as you can.

README.md

@@ -32,6 +32,10 @@ You should also add an index to ensure that the `position` column value is uniqu
 
 The above assumes that your items are scoped to a parent table called `lists`.
 
+If you have a polymorphic `belongs_to` then you'll want to add the type column to the index also:
+
+`add_index :items, [:listable_id, :listable_type, :position], unique: true`
+
 The Positioning gem uses `0` and negative integers to rearrange the lists it manages so don't add database validations to restrict the usage of these. You are also restricted from using `0` and negative integers as position values. If you try, the position value will become `1`. If you try to set an explicit position value that is greater than the next available list position, it will be rounded down to that value.
 
 ### Declaring Positioning
@@ -66,6 +70,10 @@ positioned on: :type
 belongs_to :list
 belongs_to :category
 positioned on: [:list, :category, :enabled]
+
+# If your belongs_to is polymorphic positioning will automatically add the type to the scope
+belongs_to :listable, polymorphic: true
+positioned on: :listable
 ```
 
 ### Initialising a List

lib/positioning.rb

@@ -36,6 +36,7 @@ def positioned(on: [], column: :position)
 
             if reflection&.belongs_to?
               positioning_columns[column][:scope_columns] << reflection.foreign_key
+              positioning_columns[column][:scope_columns] << reflection.foreign_type if reflection.polymorphic?
               positioning_columns[column][:scope_associations] << reflection.name
             else
               positioning_columns[column][:scope_columns] << scope_component

test/models/entity.rb

@@ -0,0 +1,5 @@
+class Entity < ActiveRecord::Base
+  belongs_to :includable, polymorphic: true
+
+  positioned on: :includable
+end

test/support/active_record.rb

@@ -13,6 +13,14 @@
       t.string :name
     end
 
+    create_table :entities, force: true do |t|
+      t.string :name
+      t.integer :position, null: false
+      t.references :includable, polymorphic: true
+    end
+
+    add_index :entities, [:includable_id, :includable_type, :position], unique: true
+
     create_table :items, force: true do |t|
       t.string :name
       t.integer :position, null: false

test/test_positioning.rb

@@ -11,6 +11,7 @@
 require_relative "models/author/teacher"
 require_relative "models/blog"
 require_relative "models/post"
+require_relative "models/entity"
 
 class TestRelativePositionStruct < Minitest::Test
   def test_struct_takes_keyword_arguments
@@ -614,6 +615,10 @@ def test_that_position_columns_will_cope_with_standard_columns
     assert_equal({position: {scope_columns: ["list_id", "enabled"], scope_associations: [:list]}}, Author.positioning_columns)
   end
 
+  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_must_have_unique_keys
     assert_raises(Positioning::Error) do
       Item.send :positioned, on: :list