Refactor GroupOrderArticle updates

[wvengen]

There are several places where GroupOrderArticles are created and/or updated. This happens in different ways. It would be healthy to consolidate that, if possible.

Let's investigate a bit and then see what makes sense.

• Member ordering just calls the group order's save_group_order_articles. Here all order articles are iterated, and at the end the group order totals are saved.
• Balancing: add & remove ordergroup for order article: this template using goa controller. Here only the result it set, as computation of who gets what is already done, and the order article's result doesn't change anymore.
• API /api/v1/group_order_articles (in PR API-4: ordering #573) does something similar as member ordering, but then per group order article.

[wvengen]

#573 (comment)

I looked it it again, and the moment when OrderArticle#update_results! and GroupOrder#update_price! are called depends on the action that is taken: if multiple products are updated in a group order, GroupOrder#update_price! only needs to be called once at the end (not each time a GroupOrderArticle is modified) - this happens in the regular member ordering screens. And when an OrderArticle is updated among multiple group orders, #update_results! only needs to be called once at the end too (we don't do this currently, as far as I know, but it could be possible).

Perhaps ideally I'd have some kind of system that queues OrderArticle#update_results! and GroupOrder#update_price! for the speciic order article and group order when a GroupOrderArticle is changed, and then at the end of the transaction, all of these queued updates are performed once. We don't have such a system currently. So I think the place for these calls is in the code that requests the GroupOrderArticle updates, which in this case is the controller.