Avoid a subquery in updating counter cache

Since UPDATE with a subquery doesn't work on MySQL.

activerecord/lib/active_record/associations/builder/belongs_to.rb

@@ -63,12 +63,7 @@ def belongs_to_counter_cache_after_update(reflection)
         private
           def counter_cache_target(reflection, model, foreign_key)
             primary_key = reflection.association_primary_key(model)
-
-            if primary_key == model.primary_key
-              foreign_key
-            else
-              model.unscoped.where!(primary_key => foreign_key)
-            end
+            model.unscoped.where!(primary_key => foreign_key)
           end
       end
     end

activerecord/lib/active_record/counter_cache.rb

@@ -111,7 +111,13 @@ def update_counters(id, counters)
           updates << sanitize_sql_for_assignment(touch_updates) unless touch_updates.empty?
         end
 
-        unscoped.where(primary_key => id).update_all updates.join(", ")
+        if id.is_a?(Relation) && self == id.klass
+          relation = id
+        else
+          relation = unscoped.where!(primary_key => id)
+        end
+
+        relation.update_all updates.join(", ")
       end
 
       # Increment a numeric field by one, via a direct SQL update.