thoughtbot / squirrel

Squirrel
======
SQL Simplification Plugin for ActiveRecord
This plugin extends the ActiveRecord::Base#find method to be able to
take a block of Ruby which will get parsed into a nice SQL string
and have its results returned.
Author::     Jon Yurek (mailto:jyurek@thoughtbot.com)
Copyright::  Copyright(c) 2008 thoughtbot, inc.
License::    Distributes under the same terms as Ruby
Website::    https://www.thoughtbot.com/projects/squirrel
Squirrel is a plugin for ActiveRecord which attempts to make SQL
querier a much more natural prospect. You can write your queries
in Ruby code and they get translated, including all proper table
joins, into relevant SQL code and executed, returning your results.
  User.find(:all) do
    first_name.contains? params[:first_name]
    posts.created_at >= 1.week.ago
  end
This query will return all Users that have a first_name that contains whatever
was passed in as the "first_name" parameter, and that has any Posts that were
created"in the past week. Both columns and associations are referenced as
methods. Columns are referenced exactly as they are in the database, and 
associations are referenced exactly as they are specified in their respective
has_many, belongs_to, etc calls. For example, in the snippet above, the User
has_many :posts, and so we use "posts" as the method to refer to that
association.
This mechanism works for *all* of ActiveRecord's associations, because it
piggybacks on AR's eager loading functionality, which always produces the
joins necessary for getting the columns required.
By default, all conditions specified in the query are ANDed together. If it is
necessary to have any condition match, you can group your conditions together
using the "any" method, which takes a block containing the conditions.
For example:
  Playlist.find(:all) do
    any do
      name == "Party Mix"
      total_length > 3600
    end
  end
... will find all Playlists that either have a name of "Party Mix" or that
have a total length of 1 hour (3600 seconds). There is also an "all" method
that works similarly, but joins with "AND". These groups are nestable."
Currenly, there is no allowance in Squirrel for either grouping or fetching
columns that aren't part of any of the included tables.