# Rails tip: Dealing with out of sync migrations

Written by Piers Cawley on

Sometimes, for one embarrassing reason or another (usually involving chaotic branch merges…) a database migration can get leapfrogged. When this happens, it’s tempting to renumber the leapfrogged migration, but that breaks any servers where the migration didn’t get renumbered. Here’s how I dealt with it recently:

 class MaybeOldMigration < ActiveRecord::Migration def self.up unless old_migration_applied? OldMigration.up end end def old_migration_applied? # Checks that the schema looks as it should # if the old migration got applied end end  Yeah, it's a hack, but it's a fairly robust hack.