Caching issue on assembly product pages (product cache key)

[jkelleyj]

Problem description

When an assembly's part is updated, it is not updating the timestamp on the assembly itself. This can cause the product page for the assembly to be out of date. The cache key on the product page in frontend relies on the cache_key of the Spree::Product. Since touching/saving a variant that is a part of the assembly does not update the assembly's updated_at timestamp, the page can be out of date, looking in stock when it is actually out of stock.

Recommended solution

In the variant decorator, we can simply add the following:

after_touch :touch_assemblies
def touch_assemblies
  self.assemblies.map(&:touch)
end

This should reliably update the assembly variant and through it the product record's updated_at timestamp. I'm not certain that this will handle deferred variant's correctly, so an approach like this may work better on the product decorator.

after_touch :touch_assemblies, if: :can_be_part?

def touch_assemblies        
  assys = self.variants_including_master.joins(:assemblies).flat_map { |v| v.assemblies }.uniq
  assys.map(&:touch)
end

If no one sees an issue with this approach, I'm happy to submit a pull request.

[jkelleyj]

The only concern I have about this solution is that it could cause infinite recursion. If a part touches an assembly that is a part of another assembly, touching it would trigger another round up the tree that could (in theory) loop back to the originating Part, causing infinite recursion.

https://github.com/spree-contrib/spree-product-assembly/blob/master/app/models/spree/product_decorator.rb#L14
This appears to prevent a variant from being both a part and an assembly, so I think the infinite recursion should never happen.