cache_child_count added using counter_cache of belongs_to :children

lib/closure_tree/acts_as_tree.rb

@@ -13,7 +13,8 @@ def acts_as_tree(options = {})
         :order,
         :parent_column_name,
         :with_advisory_lock,
-        :touch
+        :touch,
+        :cache_child_count
       )
 
       class_attribute :_ct

lib/closure_tree/model.rb

@@ -9,7 +9,8 @@ module Model
                  class_name: _ct.model_class.to_s,
                  foreign_key: _ct.parent_column_name,
                  inverse_of: :children,
-                 touch: _ct.options[:touch]
+                 touch: _ct.options[:touch],
+                 counter_cache: _ct.options[:cache_child_count] ? :child_count : false
 
       # TODO, remove when activerecord 3.2 support is dropped
       attr_accessible :parent if _ct.use_attr_accessible?

spec/counter_cache_spec.rb

@@ -0,0 +1,30 @@
+require 'spec_helper'
+
+describe 'caching child count' do
+  before do
+    @root = MenuItem.create
+  end
+
+  describe 'cache_child_count option' do
+    it 'should default to 0' do
+      expect(@root.child_count).to eq(0)
+    end
+
+    it 'should keep track of the direct children as they are added and removed' do
+      @root.children << MenuItem.new
+      expect(@root.reload.child_count).to eq(1)
+      MenuItem.create(parent: @root)
+      expect(@root.reload.child_count).to eq(2)
+      @root.children.first.destroy
+      expect(@root.reload.child_count).to eq(1)
+    end
+
+    it 'should not count children of children' do
+      child_node = MenuItem.new
+      child_node.children << MenuItem.new
+      @root.children << child_node
+
+      expect(@root.reload.child_count).to eq(1)
+    end
+  end
+end

spec/db/models.rb

@@ -103,5 +103,5 @@ class Metal < ActiveRecord::Base
 end
 
 class MenuItem < ActiveRecord::Base
-  acts_as_tree(touch: true, with_advisory_lock: false)
+  acts_as_tree(touch: true, with_advisory_lock: false, cache_child_count: true)
 end

spec/db/schema.rb

@@ -128,6 +128,7 @@
   create_table 'menu_items' do |t|
     t.string 'name'
     t.integer 'parent_id'
+    t.integer 'child_count', null: false, default: 0
     t.timestamps
   end