heroku rake db:pull --remote staging

database.rb

require 'heroku'
require 'taps/operation'

class Database
  def self.pull(*args)
    new.pull(*args)
  end

  def initialize(uri=ENV['DATABASE_URL'])
    @uri = uri
  end

  def pull(*args)
    options     = args.extract_options!
    application = args.shift
    username    = args.shift || ENV['DB_PULL_USERNAME']
    password    = args.shift || ENV['DB_PULL_PASSWORD']

    if options[:unless] == application
      raise 'Cannot pull into self.'
    else
      Session.new(application, username, password).pull(@uri)
    end
  end

  private

  class Session
    def initialize(application, username, password)
      @session = Heroku::Client.new(username, password).database_session(application)
    end

    def pull(local_uri)
      STDOUT.sync = true
      STDERR.sync = true
      Taps::Pull.new(local_uri, remote_uri, options).run
    end

    private

    def options
      { :default_chunksize => 1000, :session_uri => session_uri }
    end

    def remote_uri
      @session['url']
    end

    def session_uri
      @session['session']
    end
  end
end

databases.rake

namespace :db do
  desc "Copy production data into the current app's database."
  task :pull => :environment do
    Database.pull 'prancing-igloo-42', :unless => ENV['APP_NAME']
  end
end

Part a Rails app I'm working on. database.rb lives in lib, databases.rake in lib/tasks, of course, and I've included heroku and taps in my Gemfile.

To configure, set ENV['DB_PULL_USERNAME'] and ENV['DB_PULL_PASSWORD'] in your staging app to the credentials of a user with access to your production app, and replace prancing-igloo-42 with the name of your production app.