ERROR: Failed to build gem native extension.

I ran into a tiny pickle while installing the ibm_db gem on Ubuntu:

Select which gem to install for your platform (i486-linux)
 1. ibm_db 0.9.5 (ruby)
 2. ibm_db 0.9.5 (mswin32)
 3. ibm_db 0.9.4 (ruby)
 4. ibm_db 0.9.4 (mswin32)
 5. Skip this gem
 6. Cancel installation
> 1
Building native extensions.  This could take a while...
ERROR:  While executing gem ... (Gem::Installer::ExtensionBuildError)
    ERROR: Failed to build gem native extension.

ruby extconf.rb install ibm_db
extconf.rb:9:in `require': no such file to load -- mkmf (LoadError)
	from extconf.rb:9

The problem is that mkmf isn’t included in the base Ruby package on Ubuntu. You need need the full development package to install gems from source. Installing it solves the problem.

sudo apt-get install ruby1.8-dev

Rails and DB2 data types

When creating a table in a Rails migration, you have to specify data types using platform-agnostic names. The mapping of Rails types onto DB2 types is defined in ibm_db_adapter.rb:

:primary_key => @servertype.primary_key,
:string      => { :name => "varchar", :limit => 255 },
:text        => { :name => "clob" },
:integer     => { :name => "integer" },
:float       => { :name => "float" },
:datetime    => { :name => "timestamp" },
:timestamp   => { :name => "timestamp" },
:time        => { :name => "time" },
:date        => { :name => "date" },
:binary      => { :name => "blob" },

# A boolean can be represented  by a smallint,
# adopting the convention that False is 0 and True is 1
:boolean     => { :name => "smallint"},
:xml         => { :name => "xml"},
:decimal     => { :name => "decimal" }

Useful Resources

InfoCenter | DB2 Data Types
dW | DB2 and Ruby on Rails, Part 1 (May 2007)
dW | An Introduction to Ruby on Rails for DB2 Developers (June 2006)

The DB2 adapter is now called ibm_db. You can refresh your installation by typing gem install ibm_db at the command line and choosing the latest win32 release.