move Rails 4.2 counter cached associations destroy inside callbacks

This will allow to detect counter cached columns changes in callbacks
like `after_destroy` or `after_commit on: :destroy`.

lib/paranoia.rb

@@ -66,24 +66,20 @@ def self.extended(klazz)
   def destroy
     callbacks_result = transaction do
       run_callbacks(:destroy) do
-        touch_paranoia_column
-      end
-    end
-    if callbacks_result
-      if ActiveRecord::VERSION::STRING >= '4.2'
-        each_counter_cached_associations do |association|
-          foreign_key = association.reflection.foreign_key.to_sym
-          unless destroyed_by_association && destroyed_by_association.foreign_key.to_sym == foreign_key
-            if send(association.reflection.name)
-              association.decrement_counters
+        result = touch_paranoia_column
+        if result && ActiveRecord::VERSION::STRING >= '4.2'
+          each_counter_cached_associations do |association|
+            foreign_key = association.reflection.foreign_key.to_sym
+            unless destroyed_by_association && destroyed_by_association.foreign_key.to_sym == foreign_key
+              if send(association.reflection.name)
+                association.decrement_counters
+              end
             end
           end
         end
       end
-      self
-    else
-      false
     end
+    callbacks_result ? self : false
   end
 
   # As of Rails 4.1.0 +destroy!+ will no longer remove the record from the db

test/paranoia_test.rb

@@ -684,6 +684,32 @@ def test_counter_cache_column_update_on_really_destroy
     end
   end
 
+  def test_callbacks_for_counter_cache_column_update_on_destroy
+    parent_model_with_counter_cache_column = ParentModelWithCounterCacheColumn.create
+    related_model = parent_model_with_counter_cache_column.related_models.create
+
+    assert_equal nil, related_model.instance_variable_get(:@after_destroy_callback_called)
+    assert_equal nil, related_model.instance_variable_get(:@after_commit_on_destroy_callback_called)
+
+    related_model.destroy
+
+    assert related_model.instance_variable_get(:@after_destroy_callback_called)
+    assert related_model.instance_variable_get(:@after_commit_on_destroy_callback_called)
+  end
+
+  def test_callbacks_for_counter_cache_column_update_on_really_destroy!
+    parent_model_with_counter_cache_column = ParentModelWithCounterCacheColumn.create
+    related_model = parent_model_with_counter_cache_column.related_models.create
+
+    assert_equal nil, related_model.instance_variable_get(:@after_destroy_callback_called)
+    assert_equal nil, related_model.instance_variable_get(:@after_commit_on_destroy_callback_called)
+
+    related_model.really_destroy!
+
+    assert related_model.instance_variable_get(:@after_destroy_callback_called)
+    assert related_model.instance_variable_get(:@after_commit_on_destroy_callback_called)
+  end
+
   private
   def get_featureful_model
     FeaturefulModel.new(:name => "not empty")
@@ -746,6 +772,19 @@ class RelatedModel < ActiveRecord::Base
   acts_as_paranoid
   belongs_to :parent_model
   belongs_to :parent_model_with_counter_cache_column, counter_cache: true
+
+  after_destroy do |model|
+    if parent_model_with_counter_cache_column && parent_model_with_counter_cache_column.reload.related_models_count == 0
+      model.instance_variable_set :@after_destroy_callback_called, true
+    end
+  end
+  after_commit :set_after_commit_on_destroy_callback_called, on: :destroy
+
+  def set_after_commit_on_destroy_callback_called
+    if parent_model_with_counter_cache_column && parent_model_with_counter_cache_column.reload.related_models_count == 0
+      self.instance_variable_set :@after_commit_on_destroy_callback_called, true
+    end
+  end
 end
 
 class Employer < ActiveRecord::Base