def find_one(conditions_or_id)
      return nil if conditions_or_id.nil?
      if Hash === conditions_or_id
        Mongoid::Criteria.translate(self, conditions_or_id).one
      else
        Mongoid::Criteria.translate(self, conditions_or_id)
      end
    end
def find_one(conditions_or_id)
      return nil if conditions_or_id.nil?
      if Hash === conditions_or_id
        Mongoid::Criteria.translate(self, conditions_or_id).one
      else
        Mongoid::Criteria.translate(self, conditions_or_id)
      end
    end
Find a +Document+ based on id (+String+ or +BSON::ObjectId+)
 or conditions

 <tt>Person.find_one('1')</tt>
 <tt>Person.find_one(:conditions => {:age.gt => 25}, :order_by => [[:name,
 :asc]])</tt>