[英]Ruby on Rails - Virtual Attributes
我有以下模型:
create_table "material_costs", :force => true do |t|
t.string "material"
t.integer "height"
t.integer "width"
t.decimal "cost", :precision => 4, :scale => 2
t.datetime "created_at"
t.datetime "updated_at"
end
如何在模型中創建虛擬屬性,以給我每種材料的每平方英寸成本?
另外,我還有另一個模型來保存增值稅值:
create_table "taxes", :force => true do |t|
t.string "name"
t.decimal "rate", :precision => 10, :scale => 0
t.datetime "created_at"
t.datetime "updated_at"
end
如何使用此模型為每個物料提供每平方英寸的總價格,即需要增加增值稅率?
編輯 -我現在將增值稅值存儲在以下模型中:
create_table "app_options", :force => true do |t|
t.string "name"
t.string "value"
t.datetime "created_at"
t.datetime "updated_at"
end
編輯 -這是我的控制器代碼:
def calculate_quote
@moulding = Moulding.find( params[:id], :select => 'cost, width' )
@mount = MaterialCost.find(1).total_cost_per_square_mm
@glass = MaterialCost.find(2).total_cost_per_square_mm
@backing_board = MaterialCost.find(3).total_cost_per_square_mm
@wastage = AppOption.find( 2, :select => 'value' )
@markup = AppOption.find( 3, :select => 'value' )
respond_to do |format|
format.json { render :json => { :moulding => @moulding, :mount => @mount, :glass => @glass, :backing_board => @backing_board, :wastage => @wastage, :markup => @markup } }
end
end
將其放在表中實際上沒有任何意義,否則在每次更新時都需要重新計算。
正如Matchu所建議的,您應該只在模型類中定義一個方法。
注意:我添加了一個類變量來保存稅額。
class MaterialCost < ActiveRecord::Base
# Initialize the tax rate on initialization of the class
@@tax = AppOptions.find(:first, :name => 'VAT').value.to_f
# ...
def base_cost_per_square_inch
cost / (height * width)
end
def total_cost_per_square_inch
base_cost_per_square_inch * (1 + @@tax)
end
end
和一些控制器代碼:
class MaterialsController < ApplicationController
def calculate_full_price
# GET /Materials/calculate_full_price/5
# Get the material in question using the ID param.
material = MaterialCost.find(:first, :id => params[:id])
# Calculate the total price
@total_price_per_sq_in_with_tax = material.total_cost_per_square_inch
# Done (fall off to render the normal view)
end
end
我不太確定您的稅收用例到底是什么,但這是否更有意義?
它本身並不是真正的虛擬屬性,只是一種方法,對嗎?
def cost_per_square_inch
cost / height / width
end
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