Ruby on Rails模型中nil值的乘法

Question

I have several calculated values as part of my risk.rb model

before_save :calculate_risk
def calculate_risk
  self.risk1_total = self.component1 * self.component2 * self.component3
  self.risk2_total = self.component4 * self.component5 * self.component6
  ...
end

I want to be able to create a risk without filling out the form completely thus each of those components would be nil. So this method creates an error because * is not a valid method for a nil. What is the best way to handle this? I have considered

def calculate_risk
  if self.component1.nil? || self.component2.nil? || self.component3.nil?
    self.risk1_total = self.component1 * self.component 2 * self.component3
  elsif ...
end

However, this is obviously inefficient and repetitive. I also considered initializing all of these values, though I do not know the most efficient way of doing this.

Answer 1

You can do something like the following:

before_save :calculate_risk
def calculate_risk
  self.risk1_total = [self.component1,self.component2,self.component3].compact.inject(:*)
  self.risk2_total = [self.component4,self.component5,self.component6].compact.inject(:*)
  ...
end

This is assuming you want nil values to just be dropped from the calculation. This will give a result of nil if all values are nil . You could replace the nil s with zeroes if you prefer. You may also be interested in the :reject method or other cools tools in the Ruby Array and Enumerable classes.

I hope that helps.