Вы можете попробовать вызвать to_s для объекта.В irb:
ruby-1.9.2-p180 > p = Project.last #=> #<Project _id: 4e00e77d399a46759d000002, _type: nil, version: 1, created_at: 2011-06-21 18:48:34 UTC, updated_at: 2011-06-21 18:48:34 UTC, name: "Testing MongoDB", client_id: 3, client_name: nil, group_id: 35, requestor_id: 14, requestor_name: "Test Client User", requestor_phone: "", creator_id: 2, creator_name: "Some Guy", manager_id: 23, manager_name: "Some Other Guy", manager_phone: "", manager_email: "", active: true, status: "open", default_hourly_cost: "0.0", default_hourly_charge: "0.0", default_material_markup: "0.35", add_email_internal: "", add_email_client: "", client_po_number: "", client_ticket_number: "", date_requested: nil, date_requested(1i): "2011", date_requested(2i): "6", date_requested(3i): "21">
ruby-1.9.2-p180 > p.id.to_s #=> "4e00e77d399a46759d000002"
Если это не сработает, вы можете опубликовать свой environment.rb?