I followed DataMapper guide to install PostgreSQL adapter:
[$] sudo apt-get install postgresql-9.3 libpq-dev
Then, in my Gemfile:
(...) gem 'data_mapper' gem 'dm-postgres-adapter' (...)
Whe I tried to bundle install, I got the following error:
Gem::Ext::BuildError: ERROR: Failed to build gem native extension. /home/guida/.rvm/rubies/ruby-2.1.2/bin/ruby extconf.rb checking for main() in -lpq... yes checking for libpq-fe.h... yes checking for libpq/libpq-fs.h... yes checking for postgres.h... no *** extconf.rb failed *** Could not create Makefile due to some reason, probably lack of necessary libraries and/or headers. Check the mkmf.log file for more details. You may need configuration options.
After some research, I discovered that you need the header files for postgresql 9.3, which you can install by executing:
[$] sudo apt-get install postgresql-server-dev-9.3