counter_cache's on parents need to be updated if they are moved to an…

…other node

Ported from
saturnflyer@bac1762#diff-1
thanks Joel Junstrom

lib/acts_as_tree/active_record/acts/tree.rb

@@ -75,6 +75,8 @@ def acts_as_tree(options = {})
           class_eval <<-EOV
             include ActiveRecord::Acts::Tree::InstanceMethods
 
+            after_update :update_parents_counter_cache
+
             def self.roots
               find(:all, :conditions => "#{configuration[:foreign_key]} IS NULL",
                    :order => #{configuration[:order].nil? ? "nil" : %Q{"#{configuration[:order]}"}})
@@ -125,6 +127,15 @@ def self_and_siblings
         def self_and_children
           [self] + self.children
         end
+
+        private
+
+        def update_parents_counter_cache
+          if self.respond_to?(:children_count) && parent_id_changed?
+            self.class.decrement_counter(:children_count, parent_id_was)
+            self.class.increment_counter(:children_count, parent_id)
+          end
+        end
       end
     end
   end

test/acts_as_tree_test.rb

@@ -26,6 +26,7 @@ def setup_db
     create_table :mixins do |t|
       t.column :type, :string
       t.column :parent_id, :integer
+      t.column :children_count, :integer, :default => 0
     end
   end
 end
@@ -51,6 +52,10 @@ class TreeMixinNullify < Mixin
   acts_as_tree :foreign_key => "parent_id", :order => "id", :dependent => :nullify
 end
 
+class TreeMixinWithCounterCache < Mixin
+  acts_as_tree :foreign_key => "parent_id", :order => "id", :counter_cache => :children_count
+end
+
 class RecursivelyCascadedTreeMixin < Mixin
   acts_as_tree :foreign_key => "parent_id"
   has_one :first_child, :class_name => 'RecursivelyCascadedTreeMixin', :foreign_key => :parent_id
@@ -103,7 +108,7 @@ def test_insert
 
     assert_equal @extra.parent, @root1
 
-    assert_equal 3, @root1.children.size
+    assert_equal 3, @root1.reload.children.count
     assert @root1.children.include?(@extra)
     assert @root1.children.include?(@root_child1)
     assert @root1.children.include?(@root_child2)
@@ -193,9 +198,9 @@ def test_eager_association_loading
     roots = TreeMixin.find(:all, :include => :children, :conditions => "mixins.parent_id IS NULL", :order => "mixins.id")
     assert_equal [@root1, @root2, @root3], roots
     assert_no_queries do
-      assert_equal 2, roots[0].children.size
-      assert_equal 0, roots[1].children.size
-      assert_equal 0, roots[2].children.size
+      assert_equal 2, roots[0].children.count
+      assert_equal 0, roots[1].children.count
+      assert_equal 0, roots[2].children.count
     end
   end
 
@@ -252,3 +257,31 @@ def test_inverse_of
     assert_equal @root, @root_child.parent
   end
 end
+
+
+class TreeTestWithCounterCache < Test::Unit::TestCase
+  def setup
+    teardown_db
+    setup_db
+    @root = TreeMixinWithCounterCache.create!
+    @child1 = TreeMixinWithCounterCache.create! :parent_id => @root.id
+    @child1_child1 = TreeMixinWithCounterCache.create! :parent_id => @child1.id
+    @child2 = TreeMixinWithCounterCache.create! :parent_id => @root.id
+  end
+
+  def teardown
+    teardown_db
+  end
+
+  def test_counter_cache
+    assert_equal 2, @root.reload.children_count
+    assert_equal 1, @child1.reload.children_count
+  end
+
+  def test_update_parents_counter_cache
+    @child1_child1.update_attributes(:parent_id => @root.id)
+    assert_equal 3, @root.reload.children_count
+    assert_equal 0, @child1.reload.children_count
+  end
+
+end