Rails将属性分配给实例

Question

I am trying to calculate how much the total cost of my transaction will be. And to test I am running Transaction.last.calculate_total_payment , it is returning a BigDecimal which is what I want but none of the attributes are being updated on the instance after. What am I doing wrong?

class Transaction < ActiveRecord::Base
    has_one :auction
    has_one :bid
    belongs_to :inventory_part      
    TIER0 = 0
    TIER1 = 5_000
    TIER2 = 50_000
    TIER3 = 500_000
    TIER4 = 1_000_000
.
.
.
.

    def calculate_total_payment
    part = self.bid.part_price

    self.tax = part * self.tax_rate

    if self.bid.tx.shipping_account
        self.final_shipping_cost = 0 
    else # testing purposes
        self.final_shipping_cost = self.bid.est_shipping_cost
    end
    price_before_fees = part + self.tax + self.final_shipping_cost

    if price_before_fees < TIER1 #5,000
      self.bid_aero_fee = price_before_fees * 0.025
      self.armor_fee = price_before_fees * 0.015
    elsif price_before_fees < TIER2 #50,000
      self.bid_aero_fee = (price_before_fees - TIER1) * 0.015 + 125
      self.armor_fee = (price_before_fees - TIER1) * 0.01 + 75
    elsif price_before_fees < TIER3 #500,000
      self.bid_aero_fee = (price_before_fees - TIER2) * 0.0125 + 800
      self.armor_fee = (price_before_fees - TIER2) * 0.0075 + 525
    elsif price_before_fees < TIER4 #1,000,000
      self.bid_aero_fee = (price_before_fees - TIER3) * 0.0075 + 6425
      self.armor_fee = (price_before_fees - TIER3) * 0.005 + 3900
    else # anything over a million
        self.bid_aero_fee = (price_before_fees - TIER4) * 0.0075 + 10175
        self.armor_fee = (price_before_fees - TIER4) * 0.0035 + 6400
    end

    self.total_fee = self.armor_fee + self.bid_aero_fee
    self.total_amount = price_before_fees + self.total_fee
  end
end

Answer 1

You are never calling save in the calculate_total_payment method. You need to explicitly save the object for it to be persisted in the DB.

Answer 2

You should call save! at the end if you want to make your changes persistent in the database. Without this, it will modify the object in place (so changes will disappear after reloading of fetching the object again).