Initial counter_cache implementation

README.md

@@ -162,6 +162,26 @@ child1.ancestry_path
 => ["Grandparent", "Parent", "First Child"]
 ```
 
+### Counter cache
+
+It's possible to use Rails' counter cache option for the `parent` relationship by adding the `counter_cache: true` option to `has_closure_tree`.
+
+```ruby
+class Tag < ApplicationRecord
+  has_closure_tree counter_cache: true
+end
+```
+
+You will need to generate one additional migration:
+
+```ruby
+class AddTagsCountToTag < ActiveRecord::Migration
+  def change
+    add_column :tags, :tags_count, :integer, null: false, default: 0
+  end
+end
+```
+
 ### find_or_create_by_path
 
 You can `find` as well as `find_or_create` by "ancestry paths".

lib/closure_tree/has_closure_tree.rb

@@ -11,7 +11,8 @@ def has_closure_tree(options = {})
         :dont_order_roots,
         :numeric_order,
         :touch,
-        :with_advisory_lock
+        :with_advisory_lock,
+        :counter_cache
       )
 
       class_attribute :_ct

lib/closure_tree/model.rb

@@ -11,7 +11,9 @@ module Model
         foreign_key: _ct.parent_column_name,
         inverse_of: :children,
         touch: _ct.options[:touch],
-        optional: true)
+        optional: true,
+        counter_cache: _ct.options[:counter_cache],
+      )
 
       order_by_generations = -> { Arel.sql("#{_ct.quoted_hierarchy_table_name}.generations ASC") }
 

spec/support/models.rb

@@ -15,7 +15,7 @@ def add_destroyed_tag
 class UUIDTag < ActiveRecord::Base
   self.primary_key = :uuid
   before_create :set_uuid
-  has_closure_tree dependent: :destroy, order: 'name', parent_column_name: 'parent_uuid'
+  has_closure_tree dependent: :destroy, order: 'name', parent_column_name: 'parent_uuid', counter_cache: true
   before_destroy :add_destroyed_tag
 
   def set_uuid

spec/support/schema.rb

@@ -27,6 +27,7 @@
     t.string "title"
     t.string "parent_uuid"
     t.integer "sort_order"
+    t.integer "uuid_tags_count", default: 0, null: false
     t.timestamps null: false
   end
 

spec/support/tag_examples.rb

@@ -23,6 +23,11 @@
       expected_parent_column_name = tag_class == UUIDTag ? 'parent_uuid' : 'parent_id'
       expect(tag_class._ct.parent_column_name).to eq(expected_parent_column_name)
     end
+
+    it 'should counter_cache parent relationship' do
+      expected_counter_cache = tag_class == UUIDTag ? true : nil
+      expect(tag_class._ct.options[:counter_cache]).to be expected_counter_cache
+    end
   end
 
   describe 'from empty db' do