Testing Multiple Databases for a Rails app on Travis CI

December 13, 2011

I’m currently doing a lot of work on an open source Ruby on Rails project called Fat Free CRM. The code is hosted on github, and we are using the amazing continuous integration service provided by Travis CI.

Find out more about Travis CI here.

We’ve been working on some powerful features for Fat Free CRM, such as dynamic custom fields, and we wanted to make sure that they work across all of our supported databases. So here’s how I set up our Travis CI build matrix to test multiple databases, with some help from the Travis docs:


We add the databases to our build matrix by setting ENV variables. Add the following lines to your .travis.yml:

  - DB=mysql
  - DB=postgres
  - DB=sqlite

Database configuration

We package multiple example database configurations for each of our supported databases, like this:

  • config/database.mysql.yml
  • config/database.postgres.yml
  • config/database.sqlite.yml

We also have a rake task that is a prequisite for the spec task, and this sets up the example configuration files for Travis.

It copies the database.yml template specified by our DB variable, using postgres as the default.

FileUtils.cp "config/database.#{ENV['DB'] || 'postgres'}.yml", 'config/database.yml'


I created a new Gemfile for CI. It simply tells bundler to use the gem specified by our DB variable, prevents any other database gems from being loaded, and then loads the ‘real’ Gemfile.

Here’s the contents of Gemfile.ci:

case ENV['DB']
when "mysql"; gem "mysql2", "0.3.10"
when "sqlite"; gem "sqlite3"
when "postgres"; gem "pg", ">= 0.9.0"

def gem(*args)
  # Override 'gem' method to block any other database gems in the 'real' Gemfile
  super unless %w(pg sqlite3 mysql2).include?(args.first)

# Eval Gemfile
eval(IO.read(File.join(File.dirname(__FILE__), 'Gemfile')), binding)

That’s all there is to it.

This is a slightly unrelated topic, but I had a lot of trouble getting our new Gemfile.ci to work properly. After a serious headache, I figured out that we hadn’t updated config/boot.rb to the latest version after our upgrade. This new boot.rb had a very subtle difference, and contained the following line:

ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__)

instead of:


Notice the ||=, which meant that the BUNDLE_GEMFILE variable could actually have an effect when it was set by Travis.

You might have found this post if you are googling for Could not find multi_json-1.0.3 in any of the sources, which is the symptom that I was experiencing (due to an updated gem and an outdated Gemfile.lock). In that case, you may need to update your config/boot.rb to the latest version from Rails.