Move shipments.stock_location_id to shipping_rates.stock_location_id

[jordan-brough]

As a store with multiple stock locations, I ought to be able to present the customer with shipping rate options like this:

• Ground shipping (shipped from London)
• 2nd day air (shipped from New York)
• Same day delivery (shipped from Salt Lake City)

The bits in (...) wouldn't be shown to end users of course.

That is, each shipping rate ought to be able to come from a different stock location. Currently our data model prevents that because 1) shipments have a stock_location_id and 2) shipping rates are connected to shipping methods which can have multiple stock locations.

Would there be any problems with trying to do something like:

• Remove spree_shipments.stock_location_id
• Add spree_shipping_rates.stock_location_id
• Add this:

  class Spree::Shipment
    delegate :stock_location, to: :selected_shipping_rate, allow_nil: true
  end

?

[jordan-brough]

@alexstoick is working on this