数据迁移错误

db/migrate/20150925025200_alter_activities.rb

@@ -4,7 +4,7 @@ class AlterActivities < ActiveRecord::Migration
       if activity.act_type == 'JournalsForMessage'
         if activity.act
           unless activity.act.m_parent_id.nil?
-            parent_act = UserActivity.where("act_id = #{activity.act.parent.id} and act_type='JournalsForMessage' and container_type='Course'").first
+            parent_act = UserActivity.where("act_id = #{activity.act.m_parent_id} and act_type='JournalsForMessage' and container_type='Course'").first
             if parent_act
               parent_act.created_at = activity.act.parent.children.maximum("created_on")
               parent_act.save
@@ -21,7 +21,7 @@ class AlterActivities < ActiveRecord::Migration
         if activity.course_act_type == 'JournalsForMessage'
           if activity.course_act
             unless activity.course_act.m_parent_id.nil?
-              parent_act = CourseActivity.where("course_act_id = #{activity.course_act.parent.id} and course_act_type='JournalsForMessage'").first
+              parent_act = CourseActivity.where("course_act_id = #{activity.course_act.m_parent_id} and course_act_type='JournalsForMessage'").first
               if parent_act
                 parent_act.created_at = activity.course_act.parent.children.maximum("created_on")
                 parent_act.save
@@ -34,7 +34,7 @@ class AlterActivities < ActiveRecord::Migration
         elsif activity.course_act_type == 'Message'
           if activity.course_act
             unless activity.course_act.parent_id.nil?
-              parent_act = CourseActivity.where("course_act_id = #{activity.course_act.parent.id} and course_act_type='Message'").first
+              parent_act = CourseActivity.where("course_act_id = #{activity.course_act.parent_id} and course_act_type='Message'").first
               if parent_act
                 parent_act.created_at = activity.course_act.parent.children.maximum("created_on")
                 parent_act.save