更改code到以下

before_save :calculate_and_save_budget_contingency

def calculate_and_save_budget_contingency
  self.total_contingency = self.budget_contingency + self.risk_contingency
end

原因是 - 如果你运行在保存 after_save的您在无限循环结束：保存after_save的回调函数调用，调用保存它调用after_save的，这..

Reason for that is - if you run save in after_save you end up in infinite loop: a save calls after_save callback, which calls save which calls after_save, which...

在总体上是明智的，你使用后只能保存更改相关的模型等。

In general it's wise you use after save only for changing associated models, etc.