It should have been a simple excercise. I just wanted to set up a dev environment for a Ruby on Rails app that uses MySQL on my Snow Leopard Macbook 5.5 – easy, right? I wish… after much trial-and-error, and many encounters with the dreaded error message:

"uninitialized constant MysqlCompat::MysqlRes"

… I finally got everything to work using the following steps:

1. Installing the 64-bit version of MySQL 5.5.14 using the .dmg installer.
2. removing all possibly pre-existing versions of the mysql gem:

   sudo gem uninstall mysql

3. Installing the correct gem with the following line:

   sudo env ARCHFLAGS="-arch x86_64" gem install mysql -- --with-mysql-config=/usr/local/mysql/bin/mysql_config

4. This trick is missing from most howto’s: I needed to set the linker path.

   export DYLD_LIBRARY_PATH=/usr/local/mysql/lib/

After this, you can verify your installation is working with irb:

Motoko:project-rails karsten$ irb
>> require 'rubygems'
=> false
>> require 'mysql_api'
=> true
>> Mysql.get_client_info
=> "5.5.14"

Having done this, the rake db creation and migration tasks went smoothly.