class ActiveRecord::ConnectionAdapters::Mysql2Adapter

def new_client(config)
  Mysql2::Client.new(config)
rescue Mysql2::Error => error
  if error.error_number == ConnectionAdapters::Mysql2Adapter::ER_BAD_DB_ERROR
    raise ActiveRecord::NoDatabaseError.db_error(config[:database])
  elsif error.error_number == ConnectionAdapters::Mysql2Adapter::ER_ACCESS_DENIED_ERROR
    raise ActiveRecord::DatabaseConnectionError.username_error(config[:username])
  elsif [ConnectionAdapters::Mysql2Adapter::ER_CONN_HOST_ERROR, ConnectionAdapters::Mysql2Adapter::ER_UNKNOWN_HOST_ERROR].include?(error.error_number)
    raise ActiveRecord::DatabaseConnectionError.hostname_error(config[:host])
  else
    raise ActiveRecord::ConnectionNotEstablished, error.message
  end
end