Support composite keys

lib/positioning/mechanisms.rb

@@ -56,15 +56,19 @@ def primary_key_column
     end
 
     def primary_key
-      @positioned.send primary_key_column
+      if primary_key_column.is_a? Array
+        primary_key_column.map { |column| @positioned.send column }
+      else
+        @positioned.send primary_key_column
+      end
     end
 
     def quoted_column
       base_class.connection.quote_table_name_for_assignment base_class.table_name, @column
     end
 
     def record_scope
-      base_class.where("#{primary_key_column}": primary_key)
+      base_class.where(Array(primary_key_column).zip(Array(primary_key)).to_h)
     end
 
     def position
@@ -133,12 +137,12 @@ def solidify_position
         end
 
         relative_primary_key = if relative_record_or_primary_key.is_a? base_class
-          relative_record_or_primary_key.send(primary_key_column)
+          Array(primary_key_column).map { |column| relative_record_or_primary_key.send(column) }
         else
-          relative_record_or_primary_key
+          Array(relative_record_or_primary_key)
         end
 
-        relative_record_scope = positioning_scope.where("#{primary_key_column}": relative_primary_key)
+        relative_record_scope = positioning_scope.where(Array(primary_key_column).zip(relative_primary_key).to_h)
 
         unless relative_record_scope.exists?
           raise Error.new, "relative `#{@column}` record must be in the same scope"
@@ -154,8 +158,8 @@ def solidify_position
       unless position.is_a? Integer
         raise Error.new,
           %(`#{@column}` must be an Integer, :first, :last, ) +
-            %{before: (#{base_class.name}, #{primary_key_column}, nil, or ""), } +
-            %{after: (#{base_class.name}, #{primary_key_column}, nil or ""), nil or ""}
+            %{before: (#{base_class.name}, #{Array(primary_key_column).join(", ")}, nil, or ""), } +
+            %{after: (#{base_class.name}, #{Array(primary_key_column).join(", ")}, nil or ""), nil or ""}
       end
     end
 
@@ -176,7 +180,7 @@ def positioning_scope_was
     end
 
     def in_positioning_scope?
-      @positioned.persisted? && positioning_scope.where("#{primary_key_column}": primary_key).exists?
+      @positioned.persisted? && positioning_scope.where(Array(primary_key_column).zip(Array(primary_key)).to_h).exists?
     end
 
     def positioning_scope_changed?

test/models/item_with_composite_primary_key.rb

@@ -0,0 +1,5 @@
+class ItemWithCompositePrimaryKey < ActiveRecord::Base
+  belongs_to :list
+
+  positioned on: :list
+end

test/models/list.rb

@@ -1,5 +1,6 @@
 class List < ActiveRecord::Base
   has_many :items, -> { order(:position) }, dependent: :destroy
   has_many :item_without_advisory_locks, -> { order(:position) }, dependent: :destroy
+  has_many :item_with_composite_primary_keys, -> { order(:position) }, dependent: :destroy
   has_many :authors, -> { order(:position) }, dependent: :destroy
 end

test/support/active_record.rb

@@ -29,6 +29,16 @@
 
     add_index :item_without_advisory_locks, [:list_id, :position], unique: true
 
+    create_table :item_with_composite_primary_keys, primary_key: [:item_id, :account_id], force: true do |t|
+      t.integer :item_id, null: false
+      t.integer :account_id, null: false
+      t.string :name
+      t.integer :position, null: false
+      t.references :list, null: false
+    end
+
+    add_index :item_with_composite_primary_keys, [:list_id, :position], unique: true
+
     create_table :categories, force: true do |t|
       t.string :name
       t.integer :position, null: false

test/test_positioning.rb

@@ -3,6 +3,7 @@
 require_relative "models/list"
 require_relative "models/item"
 require_relative "models/item_without_advisory_lock"
+require_relative "models/item_with_composite_primary_key"
 require_relative "models/category"
 require_relative "models/categorised_item"
 require_relative "models/author"
@@ -175,6 +176,14 @@ def test_primary_key
     assert_equal student.id, mechanisms.send(:primary_key)
   end
 
+  def test_composite_primary_key
+    list = List.create name: "List"
+    item = list.item_with_composite_primary_keys.create item_id: "1", account_id: "1"
+
+    mechanisms = Positioning::Mechanisms.new(item, :position)
+    assert_equal item.id, mechanisms.send(:primary_key)
+  end
+
   def test_record_scope
     list = List.create name: "List"
     student = list.authors.create name: "Student", type: "Author::Student"