Question

My Rails 3.1 application connects to 2 databases, one is the default, the other is an Amazon RDS MYSQL instance.

The current database.yml contains two production database connections. The models that need to pull from the second database simply use

establish_connection "production_on_amazon"

Unfortunately Heroku overwrites your database.yml, and only seems to inlcude one database connection. Does anyone know how I can add or configure my second?

Running “heroku config” I can see there are 2 DB’s listed but cant seem to configure to connect to both. Perhaps somehow set my default to the SHARED_DATABASE_URL db on Heroku and set the alternate to the DATABASE_URL which points to Amazon…

Answer 1

Regarding Neil’s answer, here is a way to do it. Not an out-of-box solution, but might give you an idea…
/lib/active_record_extensions.rb

module ActiveRecordExtensions
  class Shard < ActiveRecord::Base
    #need to switch to the shard database connection from heroku config 
    primary_database_url = ENV['PRIMARY_DATABASE_URL']

    if(!primary_database_url.nil?)
      parsed_connection_string = primary_database_url.split("://")
      adapter = parsed_connection_string[0]
      parsed_connection_string = parsed_connection_string[1].split(":")
      username = parsed_connection_string[0]
      parsed_connection_string = parsed_connection_string[1].split("@")
      password = parsed_connection_string[0]
      parsed_connection_string = parsed_connection_string[1].split("/")  
      host = parsed_connection_string[0]
      database = parsed_connection_string[1]

      establish_connection(
        :adapter  => adapter,
        :host     => host,
        :username => username,
        :password => password,
        :database => database,
        :port     => 3306,
        :pool     => 5,
        :timeout  => 5000
      )
    else
      self.establish_connection "shard_#{Rails.env}"
    end
  end

  class ShardMigration < ActiveRecord::Migration
    def connection
      ActiveRecord::Shard.connection 
    end
  end
end

So your model should just extend ActiveRecord::Shard instead of Base