2 files changed, 19 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/associations/belongs_to_association.rb b/activerecord/lib/active_record/associations/belongs_to_association.rb
index 804a7ebf21..3e0e0d0fb9 100644
--- a/activerecord/lib/active_record/associations/belongs_to_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_association.rb
@@ -10,11 +10,22 @@ module ActiveRecord
       end
 
       def replace(record)
+        counter_cache_name = @reflection.counter_cache_column
+
         if record.nil?
+          if counter_cache_name && @owner[counter_cache_name] && !@owner.new_record?
+            @reflection.klass.decrement_counter(counter_cache_name, @owner[@reflection.primary_key_name]) if @owner[@reflection.primary_key_name]
+          end
+
           @target = @owner[@reflection.primary_key_name] = nil
         else
           raise_on_type_mismatch(record)
 
+          if counter_cache_name && @owner[counter_cache_name] && !@owner.new_record?
+            @reflection.klass.increment_counter(counter_cache_name, record.id)
+            @reflection.klass.decrement_counter(counter_cache_name, @owner[@reflection.primary_key_name]) if @owner[@reflection.primary_key_name]
+          end
+
           @target = (AssociationProxy === record ? record.target : record)
           @owner[@reflection.primary_key_name] = record.id unless record.new_record?
           @updated = true
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index b9369feeb7..32e812a86a 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -131,6 +131,14 @@ module ActiveRecord
         @association_foreign_key ||= @options[:association_foreign_key] || class_name.foreign_key
       end
 
+      def counter_cache_column
+        if options[:counter_cache] == true
+          "#{active_record.name.underscore.pluralize}_count"
+        elsif options[:counter_cache]
+          options[:counter_cache]
+        end
+      end
+
       private
         def name_to_class_name(name)
           if name =~ /::/