Question

我有一个item模型，需要计算总利润减去任何费用。我目前正在模型中做这件事。但是，我希望只有在布尔值更新为已售出时才能运行该计算。我在模型中尝试过if语句，但是没有用。

item.rb的

class Item < ActiveRecord::Base
  def profit_calc
    sold_for - bought_for - fees - shipping rescue 0
  end

  def self.purchase_total
    sum(:bought_for)
  end

  def self.fee_total
    sum(:fees)
  end

  def self.shipping_total
    sum(:shipping)
  end

  def self.sales_total
    sum(:sold_for)
  end

  def self.profit_total
    sum(:sold_for) - sum(:bought_for) - sum(:fees) - sum(:shipping)
  end

  scope :visible, -> { where(sold: false) }
  scope :sold, -> { where(sold: true) }
end

schema.rb

create_table "items", force: :cascade do |t|
  t.string   "description"
  t.float    "bought_for"
  t.float    "sold_for"
  t.float    "fees"
  t.float    "shipping"
  t.datetime "created_at",                          null: false
  t.datetime "updated_at",                          null: false
  t.boolean  "sold",                default: false
end

statistics.html.erb

<td><%= number_to_currency(@items.profit_total) %></td>

Answer 1

您可以在计算中使用sold范围：

  def self.profit_total
    sold.sum(:sold_for) - sold.sum(:bought_for) - sold.sum(:fees) - sold.sum(:shipping)
  end

但每次调用Item.profit_total时，它都会执行所有查询。如果您经常需要，可能需要缓存计算，如果已售出，则可以在after_save回调中使缓存失效。

仅在满足条件时进行Rails模型计算

1 个答案: