Merge branch 'zj-rework-migration-award-emoji' into 'master'

db/migrate/20160416182152_convert_award_note_to_emoji_award.rb

 # rubocop:disable all
 class ConvertAwardNoteToEmojiAward < ActiveRecord::Migration
-  def change
-    def up
-      execute "INSERT INTO award_emoji (awardable_type, awardable_id, user_id, name, created_at, updated_at) (SELECT noteable_type, noteable_id, author_id, note, created_at, updated_at FROM notes WHERE is_award = true)"
+  disable_ddl_transaction!
+
+  def up
+    if Gitlab::Database.postgresql?
+      migrate_postgresql
+    else
+      migrate_mysql
+    end
+  end
+
+  def down
+    add_column :notes, :is_award, :boolean
 
+    # This migration does NOT move the awards on notes, if the table is dropped in another migration, these notes will be lost.
+    execute "INSERT INTO notes (noteable_type, noteable_id, author_id, note, created_at, updated_at, is_award) (SELECT awardable_type, awardable_id, user_id, name, created_at, updated_at, TRUE FROM award_emoji)"
+  end
+
+  def migrate_postgresql
+    connection.transaction do
+      execute 'LOCK notes IN EXCLUSIVE MODE'
+      execute "INSERT INTO award_emoji (awardable_type, awardable_id, user_id, name, created_at, updated_at) (SELECT noteable_type, noteable_id, author_id, note, created_at, updated_at FROM notes WHERE is_award = true)"
       execute "DELETE FROM notes WHERE is_award = true"
+      remove_column :notes, :is_award, :boolean
     end
   end
+
+  def migrate_mysql
+    execute 'LOCK TABLES notes WRITE, award_emoji WRITE;'
+    execute 'INSERT INTO award_emoji (awardable_type, awardable_id, user_id, name, created_at, updated_at) (SELECT noteable_type, noteable_id, author_id, note, created_at, updated_at FROM notes WHERE is_award = true);'
+    execute "DELETE FROM notes WHERE is_award = true"
+    remove_column :notes, :is_award, :boolean
+  ensure
+    execute 'UNLOCK TABLES'
+  end
 end

db/migrate/20160416190505_remove_note_is_award.rb

-# rubocop:disable all
-class RemoveNoteIsAward < ActiveRecord::Migration
-  def change
-    remove_column :notes, :is_award, :boolean
-  end
-end