make schema_migrations work over multiple databases. #rails

rails_db_migrate_multiple_databases.rb

module ActiveRecord
  class Migrator
     class << self
        def get_all_versions
          table = Arel::Table.new(schema_migrations_table_name)
          # must not be Base.establish_connection b/c that'll drop the mysql2
          # adapter connection and blow up rake db:schema:dump
          SchemaMigration.establish_connection(ActiveRecord::Base.configurations['cluster'][Rails.env])
          cluster_migrations = SchemaMigration.connection.select_values(table.project(table['version'])).map{ |v| v.to_i }

          SchemaMigration.establish_connection(ActiveRecord::Base.configurations[Rails.env])
          global_migrations = SchemaMigration.connection.select_values(table.project(table['version'])).map{ |v| v.to_i }
          (cluster_migrations + global_migrations).sort
       end
     end
  end
end