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I am writing a Spree extension to allow certain items in the cart/order to be linked to each other.

A "setting" product can be associated with a "center stone" product. Eventually, there shall be constraints enforcing which things can reference each other, but that's not important yet.

Here's how I've changed the LineItem to include self references:

Spree::LineItem.class_eval do

    has_one :center_stone, class_name: "LineItem", foreign_key: "setting_id"
    belongs_to :setting, class_name: "LineItem"
end

...and the corresponding DB migration:

class AddSettingRefToLineItems < ActiveRecord::Migration
  def change
    add_reference :spree_line_items, :setting, index: true, foreign_key: true
  end
end

What I need to accomplish next is to modify the "Add to Cart" form on the product page so that an item being added to the cart can get associated with an item that is already in the cart. How do I do this?

Use Case Example

Product A and Product B are both in my cart. I am looking at the page for Product C. I want to see the options:

  • Add to Product A
  • Add to Product B
  • Add to Cart Alone

Clicking any of these options creates a Spree::LineItem for Product C as usual. If click the first two option, I also want the LineItem for Product C's setting_id to reference the LineItem for Product A in my cart.

Jessa
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  • Why do you want to add setting_id to your Product, if you actually want LineItems to reference each other? When user adds some Product C to cart with "Add to Product A" button, do you actually want Product A to be linked with (using setting_id) Product C **for all users**? – EugZol Aug 05 '15 at 17:00
  • @EugZol Sorry if I was unclear, I don't want to add anything to a Spree:Product, just to a Spree::LineItem. When speaking of products, I was referring to the instances of the Variants that are in a user's Cart. – Jessa Aug 05 '15 at 20:37
  • Okay, so your question is: how do you do such kind of things in general, or how do you make Spree use your customizations? – EugZol Aug 06 '15 at 22:32
  • @EugZol How can I make Spree use the customization? – Jessa Aug 06 '15 at 22:33
  • You should re-write Spree's view. I added plan of work as an answer. After you read the guide and try to set up the override, feel free to ask further questions, if there will be any. – EugZol Aug 06 '15 at 22:45

1 Answers1

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As was discovered, the main questions is: how to customize Spree's "add to card" function.

You need to customize views:

Deface::Override.new(:virtual_path => 'spree/products/_cart_form',
                 :name => 'centerproduct_cart_form',
                 :replace => "<what to replace>",
                 :erb => "<with what to replace>")

This should go to your app/overrides/centerproduct_cart_form.rb file (you can change name of file, just make sure name parameter in the code sample above will be changed as well to the same value).

You can figure out what to replace and with what to replace parts by looking at the source code of the view:

https://github.com/spree/spree/blob/master/frontend/app/views/spree/products/_cart_form.html.erb

EugZol
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