ensure project mirror data with post migration

db/post_migrate/20170530111134_ensure_project_mirror_data.rb

+class EnsureProjectMirrorData < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    return unless Gitlab::Database.postgresql?
+
+    execute <<-SQL
+      INSERT INTO project_mirror_data
+      SELECT id AS project_id,
+        0 AS retry_count,
+        CAST(NULL AS TIMESTAMP) AS last_update_started_at,
+        CAST(NULL AS TIMESTAMP) AS last_update_scheduled_at,
+        NOW() AS next_execution_timestamp,
+        NOW() AS created_at,
+        NOW() as updated_at
+      FROM projects
+      WHERE mirror IS TRUE
+      AND NOT EXISTS (
+        SELECT true
+        FROM project_mirror_data
+        WHERE project_mirror_data.project_id = projects.id
+      );
+    SQL
+  end
+
+  def down
+  end
+end