Modules being shared and model data

rubyonrails-talk
1

Have in a module in ./lib: module Pricing   def sell_price     (cost.to_f)/((100-(margn.to_f))/100)   end

  def sell_price_inc     ((product.cost.to_f)/((100-(product.margn.to_f))/100)*1.14)   end

  def charge_excl     (sell_price).to_f * quantity   end end

A model product: class Product < ActiveRecord::Base   include Pricing   attr_accessible :name, :code, :cost, :company_id, :margn

  belongs_to :company   has_many :allocations   has_many :companies, :through => :allocations end

An allocation model: class Allocation < ActiveRecord::Base   include Pricing   attr_accessible :company_id, :allocated_product_id, :quantity, :saledate, :cost   belongs_to :company   belongs_to :allocated_product, :class_name => 'Product' #So you have company.products and company.allocated_products. end

A products and allocations controller: class ProductsController < ApplicationController   def index     @products = Product.all   end

class AllocationsController < ApplicationController   def index     @products =Product.all     @allocations = Allocation.all   end

And the views in product index:

      <td><%=h (sprintf( "R%.02f" ,product.sell_price)) %></td>       <td><%=h (sprintf( "R%.02f" ,product.sell_price_inc)) %></td>

The above works well !

However in my allocations model and view I am trying to show the price based on quantity:   def charge_excl     (sell_price).to_f * quantity   end

I get the error: undefined local variable or method `cost'

It is obviously failing as it cannot get access to the cost parameter and its not accessible

So in a nutshell I can run calculations on one model (product) in the module but as soon as I require a calculation using two models data (cost, margin and quantity) it fails

Help is appreciated thanks

2 
 &lt;td&gt;&lt;%=h \(sprintf\( &quot;R%\.02f&quot; ,product\.sell\_price\)\) %&gt;&lt;/td&gt;
 &lt;td&gt;&lt;%=h \(sprintf\( &quot;R%\.02f&quot; ,product\.sell\_price\_inc\)\) %&gt;&lt;/td&gt;

The above works well !

I don't see how it does when you access "product.cost.to_f" in the sell_price_inc method... when you include that module in Product, it must be expecting an instance to have an attribute or method called "product" too (so a chain that looks like "product.product.cost.to_f").... do you have some other methods you didn't include in your example?

However in my allocations model and view I am trying to show the price I get the error: undefined local variable or method `cost'

You specify "attr_accessible :cost" in Allocation, but does the table have a cost field? If not, how about adding a cost method to Allocation that returns the product.cost? This would allow the included module methods to have methods that respond to the calls they're making...

3

Micheal I made an error in my post, the Module Pricing looks like:   def sell_price     (cost.to_f)/((100-(margn.to_f))/100)   end

  def sell_price_inc     ((cost.to_f)/((100-(margn.to_f))/100)*1.14)   end

They do both work for the Product model, well spotted!

"You specify "attr_accessible :cost" in Allocation, but does the table have a cost field? If not, how about adding a cost method to Allocation that returns the product.cost? This would allow the included module methods to have methods that respond to the calls they're making..."

The Allocation table has no cost field only the Product table What would the method look like? Would it go in the Allocation model, and how can I access the Product model to get access to it?

Thanks

4

Think I am on the right track as I can attain the cost through the console but the way to handle the method is what I dont get and where to put it and when to call it

a = Allocation.first

=> #<Allocation id: 1, company_id: 1, allocated_product_id: 1, quantity: 2, saledate: nil>

a.allocated_product.cost

=> #<BigDecimal:b6f12d20,'0.2222E4',4(12)>

5

Just put a method in Allocation like this:

  def cost     raise "put some error handling in for when no allocated product exists" unless self.allocated_product     self.allocated_product.cost   end

When the module calls for "cost" when it's included in Product, it will use the attribute. When it's included in Allocation it will use the new method (which delegates down to the allocated_product's cost).