Ruby on rails 在状态机转换后发送电子邮件

我正在尝试使用Rails 4.1构建一个小型费用跟踪应用程序。当用户提交费用申请时，其状态默认标记为挂起。管理员必须批准该请求。我用状态机gem来做这个

我想在请求被批准或拒绝后发送一封电子邮件，我尝试了以下模型方法：

state_machine initial: :pending do
        state :pending
        state :approved
        state :rejected
        #after_transition :on => :approved do |expense, transition|
            #expense.send_expense_approved_email
        #end

        #after_transition :on => :rejected do |expense, transition|
            #expense.send_expense_approved_email
        #end
         after_transition :on => :approved, :do => :send_expense_approved_email
         after_transition :on => :rejected, :do => :send_expense_declined_email


        event :approved do
            transition [:pending, :rejected] => :approved
        end

        event :rejected do
            transition [:pending, :approved] => :rejected
        end
    end

    def expense_amount
        items.to_a.sum { |item| item.amount }
    end

    def send_expense_approved_email
        ExpenseMailer.expense_approved(expense).deliver
    end

    def send_expense_declined_email
        ExpenseMailer.expense_declined(expense).deliver
    end
end

---

虽然状态转换成功，但我无法触发电子邮件。我已经在控制器操作中测试了邮件程序，它们发送得很好。我如何让它工作？

这些模型方法不起作用。因此，使用if和else语句检查状态，然后在更新操作中触发电子邮件。不确定，如果这是Rails的方式，但是，它正在工作