what should this do?

require 'spira'
require 'rdf/ntriples'

class Person
  include Spira::Resource

  property :name, :predicate => FOAF.name
  property :nick, :predicate => FOAF.nick
end

repository = RDF::Repository.load('http://datagraph.org/jhacker/foaf.nt')

Spira.add_repository(:default, repository)

Person.repository.object_id == repository.object_id
# => true

jhacker = Person.create('http://datagraph.org/jhacker/#self')
jhacker.save!

# Error, or equivalent to find?

jhacker = Person.create('http://datagraph.org/jhacker/#self', :nick => "some new nick, different than what's in the repository")
jhacker.save!

# Error, or equivalent to find and setting the nick?