1 files changed, 36 insertions, 0 deletions
diff --git a/db/post_migrate/20191115115043_migrate_epic_mentions_to_db.rb b/db/post_migrate/20191115115043_migrate_epic_mentions_to_db.rb
new file mode 100644
index 00000000000..97f2e568a7e
--- /dev/null
+++ b/db/post_migrate/20191115115043_migrate_epic_mentions_to_db.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+class MigrateEpicMentionsToDb < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  DELAY = 2.minutes.to_i
+  BATCH_SIZE = 10000
+  MIGRATION = 'UserMentions::CreateResourceUserMention'
+
+  JOIN = "LEFT JOIN epic_user_mentions on epics.id = epic_user_mentions.epic_id"
+  QUERY_CONDITIONS = "(description like '%@%' OR title like '%@%') AND epic_user_mentions.epic_id is null"
+
+  class Epic < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'epics'
+  end
+
+  def up
+    return unless Gitlab.ee?
+
+    Epic
+      .joins(JOIN)
+      .where(QUERY_CONDITIONS)
+      .each_batch(of: BATCH_SIZE) do |batch, index|
+      range = batch.pluck(Arel.sql('MIN(epics.id)'), Arel.sql('MAX(epics.id)')).first
+      BackgroundMigrationWorker.perform_in(index * DELAY, MIGRATION, ['Epic', JOIN, QUERY_CONDITIONS, false, *range])
+    end
+  end
+
+  def down
+    # no-op
+  end
+end