DataMapper 保存失败但没有错误

Question

当我尝试使用 DataMapper 修改并保存模型时，出现 SaveFailure 异常，但没有错误。

具体来说，我看到这条消息： “MonthlyBill#save 返回 false，MonthlyBill 未保存”

这是执行保存的代码：

post '/monthly_bills' do
  with_authenticated_user do |user|
  description = params[:description]
  expected_amount = params[:expected_amount]
  pay_period = params[:pay_period]

  monthly_bill = MonthlyBill.new(:description=>description, :expected_amount=>expected_amount, :pay_period=>pay_period)
  user.monthly_bills << monthly_bill
  user.save
end

用户模型：

class User
  include DataMapper::Resource

  property :id,             Serial
  property :email_address,  String
  property :password,       String

  has n, :monthly_bills
  has 1, :current_pay_period
end

MonthlyBill 模型：

class MonthlyBill
  include DataMapper::Resource

  property :id,             Serial
  property :description,    String
  property :expected_amount,Decimal
  property :pay_period,     Integer

  belongs_to :user
end

问题是什么，更重要的是，如何让 DataMapper 更具体地告诉我出了什么问题？

Answer 1

嗯 - 那些资本化的财产对我来说看起来令人担忧。我会做...

has n, :monthly_bills 
has 1, :current_pay_period #do you really have a CurrentPayPeriod model?!

然后尝试：

monthly_bill = MonthlyBill.new(:description=>description,:expected_amount=>expected_amount, :pay_period=>pay_period, :user=>user)
monthly_bill.save