readme

DataMapper finders are supposed to be chainable, so that 
Model.all(:conditions).all(:conditions).all(:conditions) or 
equivalent should only perform one query.  Additionally, (and 
I can't find it in the docs) chained finders also have access 
to class methods, such that Finger.all(...).long (given the 
above code) still returns a valid chained association.

http://datamapper.org/doku.php?id=docs:associations#finders_off_associations suggests that associations should also return chainable finders, which 
it does.  @hand.fingers.all(...) seems to work just fine.  
However, @hand.fingers.long, which I expect to work, seems to 
be running two queries - one on just the association (which 
is never used) and then another when the final chained 
association is used.

association_finder_bug.rb

require 'rubygems'
require 'dm-core'

DataMapper.setup(:default, 'sqlite3::memory:')

class Hand
  include DataMapper::Resource
  property :id, Serial
  has n, :fingers
end

class Finger
  include DataMapper::Resource
  property :id, Serial
  property :name, String
  belongs_to :hand
  
  def self.long
    all(:conditions => ["name <> ?", 'thumb'])
  end
end

DataMapper.auto_migrate!

hand = Hand.new()
hand.save
hand.fingers.build(:name => 'thumb').save
hand.fingers.build(:name => 'index').save
hand.fingers.build(:name => 'middle').save
hand.fingers.build(:name => 'ring').save
hand.fingers.build(:name => 'pinky').save

DataObjects::Sqlite3.logger = DataObjects::Logger.new(STDOUT, :debug)

hand = Hand.first
# SELECT "id" FROM "hands" ORDER BY "id" LIMIT 1

puts
p hand.fingers.all(:conditions => ["name <> ?", 'thumb']).map{|finger| finger.name}
# SELECT "id", "name", "hand_id" FROM "fingers" WHERE ("hand_id" IN (1)) AND name <> 'thumb' ORDER BY "id"

puts
p hand.fingers.long.map{|finger| finger.name}
# SELECT "id", "name", "hand_id" FROM "fingers" WHERE ("hand_id" IN (1)) ORDER BY "id"
# SELECT "id", "name", "hand_id" FROM "fingers" WHERE ("hand_id" = 1) AND name <> 'thumb' ORDER BY "id" DESC