Refactor counter cache to extract `decrement_counters_before_last_save` on the belongs_to association

1 files changed, 6 insertions, 37 deletions

diff --git a/activerecord/lib/active_record/associations/builder/belongs_to.rb b/activerecord/lib/active_record/associations/builder/belongs_to.rb
index 374247ffec..5e18f0e16f 100644
--- a/activerecord/lib/active_record/associations/builder/belongs_to.rb
+++ b/activerecord/lib/active_record/associations/builder/belongs_to.rb
@@ -21,47 +21,16 @@ module ActiveRecord::Associations::Builder # :nodoc:
       add_default_callbacks(model, reflection)       if reflection.options[:default]
     end
 
-    def self.define_accessors(mixin, reflection)
-      super
-      add_counter_cache_methods mixin
-    end
-
-    def self.add_counter_cache_methods(mixin)
-      return if mixin.method_defined? :belongs_to_counter_cache_after_update
-
-      mixin.class_eval do
-        def belongs_to_counter_cache_after_update(reflection)
-          if association(reflection.name).target_changed?
-            if reflection.polymorphic?
-              model_was = attribute_before_last_save(reflection.foreign_type).try(:constantize)
-            else
-              model_was = reflection.klass
-            end
-
-            foreign_key_was = attribute_before_last_save(reflection.foreign_key)
-            cache_column = reflection.counter_cache_column
-
-            association(reflection.name).increment_counters
-
-            if foreign_key_was && model_was < ActiveRecord::Base
-              counter_cache_target(reflection, model_was, foreign_key_was).update_counters(cache_column => -1)
-            end
-          end
-        end
-
-        private
-          def counter_cache_target(reflection, model, foreign_key)
-            primary_key = reflection.association_primary_key(model)
-            model.unscoped.where!(primary_key => foreign_key)
-          end
-      end
-    end
-
     def self.add_counter_cache_callbacks(model, reflection)
       cache_column = reflection.counter_cache_column
 
       model.after_update lambda { |record|
-        record.belongs_to_counter_cache_after_update(reflection)
+        association = association(reflection.name)
+
+        if association.target_changed?
+          association.increment_counters
+          association.decrement_counters_before_last_save
+        end
       }
 
       klass = reflection.class_name.safe_constantize