You have specified Item.has(:derivatives) with :class_name => "Item". You probably also want to specify the :child_key option.
You have specified Item.has(:materials) with :class_name => "Item". You probably also want to specify the :child_key option.
Producing Recipes
Sun, 30 Nov 2008 13:03:45 GMT ~ debug ~ SELECT "name" FROM "items" WHERE ("name" = 'Water') ORDER BY "name" LIMIT 1
Sun, 30 Nov 2008 13:03:45 GMT ~ debug ~ SELECT "id", "type", "product_name" FROM "bags" WHERE ("type" IN ('Recipe')) AND ("product_name" IN ('Water')) ORDER BY "id"
[]
/home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/adapters/data_objects_adapter.rb:48:in `execute_reader': ERROR:  missing FROM-clause entry for table "stacks" (PostgresError)
LINE 1: ...OM "bags" INNER JOIN "items" ON ("items"."name" = "stacks"."...
                                                             ^
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/adapters/data_objects_adapter.rb:48:in `read_many'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/adapters/data_objects_adapter.rb:173:in `with_connection'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/adapters/data_objects_adapter.rb:40:in `read_many'
	from /home/hagabaka/.ruby/gems/gems/extlib-0.9.8/lib/extlib/lazy_array.rb:89:in `[]'
	from /home/hagabaka/.ruby/gems/gems/extlib-0.9.8/lib/extlib/lazy_array.rb:89:in `lazy_load'
	from /home/hagabaka/.ruby/gems/gems/extlib-0.9.8/lib/extlib/lazy_array.rb:13:in `freeze'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/associations/relationship_chain.rb:28:in `get_children'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/associations/relationship.rb:172:in `with_repository'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/support/kernel.rb:6:in `repository'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core.rb:181:in `repository'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/repository.rb:44:in `scope'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core.rb:181:in `repository'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/support/kernel.rb:6:in `repository'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/associations/relationship.rb:172:in `with_repository'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/associations/relationship_chain.rb:25:in `get_children'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/associations/one_to_many.rb:251:in `children'
	from /home/hagabaka/.ruby/gems/gems/dm-core-0.9.7/lib/dm-core/associations/one_to_many.rb:309:in `method_missing'
	from test.rb:6:in `p'
	from test.rb:6
Consuming Recipes
Sun, 30 Nov 2008 13:03:45 GMT ~ debug ~ SELECT "name" FROM "items" WHERE ("name" = 'Water') ORDER BY "name" LIMIT 1
Sun, 30 Nov 2008 13:03:45 GMT ~ debug ~ SELECT "bags"."id", "bags"."type", "bags"."product_name" FROM "bags" INNER JOIN "items" ON ("items"."name" = "stacks"."item_name") WHERE ("bags"."type" IN ('Recipe')) AND ("stacks"."item_name" = 'Water') GROUP BY "bags"."id", "bags"."type", "bags"."product_name" ORDER BY "bags"."id"
Sun, 30 Nov 2008 13:03:45 GMT ~ error ~ ERROR:  missing FROM-clause entry for table "stacks"
LINE 1: ...OM "bags" INNER JOIN "items" ON ("items"."name" = "stacks"."...
                                                             ^