Wrapper/helper for ActiveRecord <tt>find(:all, *args)</tt>. Returns a collection of 
objects injected into a Hash. The attribute used as a key for the Hash should be
specified as first argument. if :fetch is not specified in the arguments the whole
object will be assigned as value, otherwise only the attribute spefified.
You can pass in all the same arguments to this method as you can to <tt>find(:all)</tt>.

==== Example

Given the models:

Feed(id: integer, state: string, name: string)
Post(id: integer, feed_name: string, title: string, url: string)

count the number of posts of every state. Row count is too high to use SQL JOIN.

@post_per_state = {}
feeds  = Feed.hash_all('feed_name', :fetch => 'state')
posts  = Post.all(:select      => 'COUNT(id), feed_name',
                  :group       => 'feed_name')
posts.each do |p|
  @post_per_state[feeds[p.feed_name]] ||= 0
  @post_per_state[feeds[p.feed_name]] += p.attributes['COUNT(id)'].to_i
end

=> {"new york"=>6, "georgia"=>11, "new mexico"=>2, ... }