I am starting in Rails 3. I have a simple situation where i would select a parent based on a condition of one of its children. Normally i would write something like:

Distributor.find_by_sql("select d.*, c.rate from distributors d, coverages c
        where c.country_code_id = 25 and c.distributor_id=d.id
        order by rate asc")

Although this works, it is not the best solution to take. For one, it is vulnerable to sql-injection and secondly it shows a lot of the underlying database structure, and on top of that the sql-implementation could change between databases.

In Rails 3 i can now write

Distributor.includes(:coverages).where("coverages.country_code_id=? and distributors.id =coverages.distributor_id", 25).order(:rate)

This is so readable! Awesome :)