Instead of relying on Spree::Order#outstanding_balance we make us of the
result set `balance_value` computed column. So, we ask PostgreSQL to
compute it instead of Ruby and then serialize it from that computed
column. That's a bit faster to compute that way and let's reuse logic.
We hide this new implementation under this features' toggle so it's only
used when enabled. We want hit the old behaviour by default.
This makes it possible to deploy it without releasing it to users since
the toggle is not enabled for anyone.
It aims to make the balance calculation consistent across pages.
This query object is meant to be reusable but those includes are
context-specific and will likely not be needed when reusing the query
elsewhere. If we keep them there, chances are next dev might not notice
it and will introduce a performance regression.
It's simpler and many orders of magnitude more efficient to ask the DB
to aggregate the customer balance based on their orders. It removes
a nasty N+1.
The resulting SQL query is:
```sql
SELECT customers.*, SUM(spree_orders.total - spree_orders.payment_total) AS balance
FROM "customers"
INNER JOIN "spree_orders"
ON "spree_orders"."customer_id" = "customers"."id"
WHERE "customers"."enterprise_id" = 1
AND (completed_at IS NOT NULL)
AND (state != 'canceled')
GROUP BY customers.id
ORDER BY email;
```
I'm not sure why this spec started failing. Fixes:
```
Spree::OrdersController viewing cart when an item is in the cart the page provides the right registration path
Failure/Error: expect(subject.registration_path).to eq registration_path
ActionController::UrlGenerationError:
No route matches {:action=>"index", :controller=>"registration"}
# ./spec/controllers/spree/orders_controller_spec.rb:140:in `block (5 levels) in <top (required)>'
```
DEPRECATION WARNING: `#deliver` is deprecated and will be removed in Rails 5. Use `#deliver_now` to deliver immediately or `#deliver_later` to deliver through Active Job.
Sometimes the objects are not paginated. In this case we need to avoid trying to render pagination data, as it will throw an error. This guard clause also means we can remove messy conditionals from several controllers.
