Arel is a Relational Algebra for Ruby. It simplifies the generation complex of SQL queries and it adapts to various RDBMS systems.

Arel is a Relational Algebra for ruby. It simplifies the generation complex of SQL queries and it adapts to various RDBMS systems. More info on project's page. The Arel gem is supported in /questions/tagged/ruby-on-rails framework versions 3.0 and up, however for the 2nd version of Rails the fake_arel gem shell be used.