Question

I’m a completely new rails developer so bear with me 🙂

I have two models named Product and ProductPrice in rails.

This is how ProductPrices looks:

class CreateProductPrices < ActiveRecord::Migration
  def change
    create_table :product_prices do |t|
      t.integer :product_id
      t.date :since
      t.decimal :price
      t.boolean :current

      t.timestamps
    end
  end
end

And this is how the model looks:

class ProductPrice < ActiveRecord::Base
  belongs_to :product
  attr_accessible :current, :price, :product_id, :since
end

Now I want the price to be accesible through the Product. It should always show the current price (there can be only one current price/product. The user should also be able to edit the price through product. If the price has changed in an update of the Product then a new ProductPrice should be inserted with current = true and since = the current date. The old ProductPrice should no longer be current.

I already found articles about Nested Attributes and I think that would be the way to go. Can anyone tell me how I should go about to do this?

EDIT: Thanks for the reply, I tried implementing as you said, I have this now in product.rb:

class Product < ActiveRecord::Base
  belongs_to :menu_category
  belongs_to :menu
  has_many :product_prices, :dependent => :delete_all

  scope :latest_price, lambda {product_prices.where("since <= ?",DateTime.now).order(:since).last}
  attr_accessible :active, :descFR, :descNL, :image, :menu_category_id, :menu_id, :nameFR, :nameNL
  mount_uploader :image, ImageUploader    
end

And in my index page of products I have:

<tbody>
  <% @products.each do |product| %>
  <tr>
        <td><%= product.nameNL %></td>
        <td><%= product.nameFR %></td>
        <td><%= product.descNL %></td>
        <td><%= product.descFR %></td>
        <td><%= product.latest_price.price.to_s %></td>

I also tried: product.latest_price.price or product.latest_price
I also tried addint the latest_price to attr_accessible

But I always get this error:

undefined method `latest_price' for #<Product:0x49e1e48>

EDIT2: It now works. I also found out that If I add this:

  def latest_price=(val)
    pp = ProductPrice.where(:product_id => self.id, :since => DateTime.now.to_date).first_or_create(:price => val)
    pp.price = val
    pp.save
  end

Then it completely does what I asked for in the question.

Answer 1

I assume you have a Product model. Make sure you have the following in your model:

class Product < ActiveRecord::Base
  has_many :product_prices

  def latest_price
    product_prices.where("since <= ?",DateTime.now).order(:since).last
  end
end

Now you can access all prices with:

@product.find(123)
@product.product_prices.each do |price|
  # each price for the product found here
end

But to access the latest price, the method gives you:

@product.latest_price.price # latest price
@product.latest_price.since # when the latest price was active since

Notice I added the where("since <= ?",DateTime.now). That lets you schedule prices in advance (if since is in the future).

To add a new price to the product:

@new_price = ProductPrice.create(:price => ?,
                                 :product_id => @product.id,
                                 :since => DateTime.now)

Another way to add a price to the product:

@new_price = ProductPrice.create(:price => ?, :since => DateTime.now)
@product.product_prices.push(@newprice)
@product.save

Or:

@product.product_prices << @newprice # this autosaves