Rolling back a failed Rails migration

Question

How do you roll back a failed rails migration? I would expect that rake db:rollback would undo the failed migration, but no, it rolls back the previous migratio

Answer 1

The easy way to do this is to wrap all of your actions in a transaction:

class WhateverMigration < ActiveRecord::Migration

 def self.up
    ActiveRecord::Base.transaction do
...
    end
  end

  def self.down
    ActiveRecord::Base.transaction do
...
    end
  end

end

As Luke Francl noted, "MySql['s MyISAM tables don't] support transactions" -- which is why you might consider avoiding MySQL in general or at least MyISAM in particular.

If you're using MySQL's InnoDB, then the above will work just fine. Any errors in either up or down will back out.

BE AWARE some types of actions cannot be reverted via transactions. Generally, table changes (dropping a table, removing or adding columns, etc.) cannot be rolled back.