update timestamp on discussions when merging users

fixes CNVS-12782

discussions cache some material in the "materialized view". that
material may include references to the use being deleted in a user
merge. the source material was already being updated correctly by the
merge, but the materialized view was not expiring. updating the
updated_at on the appropriate topics will force the necessary
materialized views to be refreshed.

test-plan:
 - create two distinct users, A and B
 - as user A, create a discussion topic
 - as user B, create a second discussion topic
 - as user A, reply to user B's discussion topic
 - merge user A into user B
 - view the first discussion topic; user B should display as the author
 - view the second discussion topic; user B should display as the
   reply's author

Change-Id: I48948e171b6645a371e92c8413fa289695d3d1a2
Reviewed-on: https://gerrit.instructure.com/34445
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Joel Hough <joel@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Jacob Fugal <jacob@instructure.com>

lib/user_merge.rb

@@ -144,11 +144,23 @@ class UserMerge
         end
       end
       from_user.all_conversations.find_each { |c| c.move_to_user(target_user) } unless Shard.current != target_user.shard
+
+      # all topics changing ownership or with entries changing ownership need to be
+      # flagged as updated so the materialized views update
+      begin
+        entries = DiscussionEntry.where(user_id: from_user)
+        DiscussionTopic.where(id: entries.select(['discussion_topic_id'])).update_all(updated_at: Time.now.utc)
+        entries.update_all(user_id: target_user.id)
+        DiscussionTopic.where(user_id: from_user).update_all(user_id: target_user.id, updated_at: Time.now.utc)
+      rescue => e
+        Rails.logger.error "migrating discussions failed: #{e.to_s}"
+      end
+
       updates = {}
       ['account_users', 'access_tokens', 'asset_user_accesses',
        'attachments',
        'calendar_events', 'collaborations',
-       'context_module_progressions', 'discussion_entries', 'discussion_topics',
+       'context_module_progressions',
        'group_memberships', 'page_comments',
        'rubric_assessments',
        'submission_comment_participants', 'user_services', 'web_conferences',

spec/lib/user_merge_spec.rb

@@ -352,6 +352,35 @@ describe UserMerge do
       new_attachment = user2.attachments.not_deleted.detect{|a| a.md5 == attachment2.md5}
       new_attachment.display_name.should_not == "test.txt" # attachment2 should be copied and renamed because it has unique file data
     end
+
+    it "should move discussion topics and entries" do
+      topic = course1.discussion_topics.create!(user: user2)
+      entry = topic.discussion_entries.create!(user: user2)
+
+      UserMerge.from(user2).into(user1)
+
+      topic.reload.user.should == user1
+      entry.reload.user.should == user1
+    end
+
+    it "should freshen moved topics" do
+      topic = course1.discussion_topics.create!(user: user2)
+      now = Time.at(5.minutes.from_now.to_i) # truncate milliseconds
+      Timecop.freeze(now) do
+        UserMerge.from(user2).into(user1)
+        topic.reload.updated_at.should == now
+      end
+    end
+
+    it "should freshen topics with moved entries" do
+      topic = course1.discussion_topics.create!(user: user1)
+      entry = topic.discussion_entries.create!(user: user2)
+      now = Time.at(5.minutes.from_now.to_i) # truncate milliseconds
+      Timecop.freeze(now) do
+        UserMerge.from(user2).into(user1)
+        topic.reload.updated_at.should == now
+      end
+    end
   end
 
   it "should update account associations" do