dm-fail.rb

require "rubygems"
require "dm-core"

class User
  include DataMapper::Resource
  
  has 1, :event
  
  property :username,         String, :key => true, :unique => true
 
  def eid=(eid)
    event = Event.first_or_create( :eid => eid , :user_username => username )
  end
  
end

class Event
  include DataMapper::Resource
  
  belongs_to :user

  property :id,               Serial
  property :eid,              String

end

DataMapper::Logger.new(STDOUT)
DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/test.db")
DataMapper.auto_migrate!

u = { :username => "foo", :eid => "123" }
User.first_or_create( u ) # Works fine
User.first_or_create( u ) # Fails with: ArgumentError: condition :eid does not map to a property or relationship in User