Just a quick tip:
If you’re having trouble getting do_mysql to install on Mac OS X. Try the following:
$ locate mysql_config /usr/local/mysql/bin/mysql_config
The directory /usr/local/mysql above is your mysql directory. Then try to install do_mysql with the following command (split for readability):
$ gem install do_mysql -- \ --with-mysql-dir="/usr/local/mysql/" \ --with-mysql-config="/usr/local/mysql/bin/mysql_config"
This solution was found here. I experienced the problem while trying to get merb to run with datamapper on mysql.