class Dinner
  include Mongoid::Document
  include Mongoid::Timestamps

  field :title, :type => String
  field :description, :type => String
  field :hosted_by, type => String
  field :contact_phone, type => String
  field :address, type => String

  references_one :country

  validates_presence_of :title
end


class Country
  include Mongoid::Document
  field :name, :type => String
  referenced_in :dinner

  validates_presence_of :name
end

= form_for @dinner do |f|
...
.field
    = f.label :country
    = f.select :country, Country.find(:all).collect{ |c| [c.name,c.id]}