Using Rails Migration on different database than standard “production” or “development”

Question

I have a rails project running that defines the standard production:, :development and :test DB-connections in config/database.yml

In addition I have a quiz_developm

Answer 1

For Rails 3.2, this is what we did, works with migrating up and down:

class CreateYourTable < ActiveRecord::Migration

  def connection
    @connection ||= ActiveRecord::Base.connection
  end

  def with_proper_connection
    @connection = YourTable.connection
    yield
    @connection = ActiveRecord::Base.connection
  end


  def up
    with_proper_connection do
      create_table :your_table do |t|
      end
    end
  end

  def down
    with_proper_connection do
      drop_table :your_table
    end
  end

end

Answer 2

In rails 3.2, adding a connection method to your migration does NOT work. So all of the answers like

def connection
 @connection ||= ActiveRecord::Base.establish_connection
end

simply won't work (can't down, doesn't work with change, connection lost, etc.) The reason for this is that the ActiveRecord::Migration and Migrator class have connections hard-coded to ActiveRecord::Base all over the place.

Fortunately this post pointed me to this ticket which has a good solution, namely overriding the actual rake task.

I ended up using a slightly different rake task so that I could be specific about the migrations I run on the different database (we were trying to support multiple db versions):

Here's my lib/task/database.rake

# Augment the main migration to migrate your engine, too.
task 'db:migrate', 'nine_four:db:migrate'

namespace :nine_four do
    namespace :db do
        desc 'Migrates the 9.4 database'
        task :migrate => :environment do
            with_engine_connection do
                ActiveRecord::Migrator.migrate("#{File.dirname(__FILE__)}/../../nine_four/migrate", ENV['VERSION'].try(:to_i))
            end
        end
    end
end

# Hack to temporarily connect AR::Base to your engine.
def with_engine_connection
    original = ActiveRecord::Base.remove_connection
    ActiveRecord::Base.establish_connection("#{ Rails.env }_nine_four")
    yield
ensure
    ActiveRecord::Base.establish_connection(original)
end

This allows us to put migrations specific to one database in their own subdirectory (nine_four/migrations instead of db/migrations). It also gives each database total isolation in terms of their schema and migration versions. The only downside is having two rake tasks to run (db:migrate and nine_four:db:migrate).