staging:
  adapter: <%= ENV['DATABASE_ADAPTER'] %>
  encoding: <%= ENV['DATABASE_ENCODING'] %>
  database: <%= ENV['DATABASE'] %>
  host: <%= ENV['DATABASE_HOST'] %>
  port: <%= ENV['DATABASE_PORT'].to_i %>
  pool: <%= ENV['DATABASE_POOL'].to_i %>
  username: <%= ENV['DATABASE_USERNAME'] %>
  password: <%= ENV['DATABASE_PASSWORD'] %>

/usr/local/lib/ruby/gems/2.1.0/gems/activesupport-4.2.1/lib/active_support/dependencies.rb:274:in
`require': Could not load 'active_record/connection_adapters/<%= ENV['DATABASE_ADAPTER'] %>_adapter'.
Make sure that the adapter in config/database.yml is valid. If you use an adapter other than 'mysql', 'mysql2', 'postgresql' or 'sqlite3'
add the necessary adapter gem to the Gemfile. (LoadError)

def database_configuration
    yaml = Pathname.new(paths["config/database"].existent.first || "")

    config = if yaml.exist?
      require "yaml"
      require "erb"
      YAML.load(ERB.new(yaml.read).result) || {}
    elsif ENV['DATABASE_URL']
      # Value from ENV['DATABASE_URL'] is set to default database connection
      # by Active Record.
      {}
    else
      raise "Could not load database configuration. No such file - #{yaml}"
    end

    config
  rescue Psych::SyntaxError => e
    raise "YAML syntax error occurred while parsing #{paths["config/database"].first}. "
          "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. "
          "Error: #{e.message}"
  rescue => e
    raise e, "Cannot load `Rails.application.database_configuration`:n#{e.message}", e.backtrace
  end