I used the new profiler tools on this page, and noticed a lot of
allocations in the Globalize library, which we use for translating
database records. I realized that we were loading all of the fields of
not just all of the items on the page, but all of their translation
records in all locales! We used to scrape data for lots of languages, so
that can be quite a lot!
Unfortunately, Rails's `includes` method to efficiently preload related
records always loads all fields, and simply can't be overridden.
So, in this change we write manual preloading code, to identify the
records we need, load them in big bulk queries, and assign them back to
the appropriate associations. Basically just what `includes` does, but
written out a bit more, to give us the chance to specify SELECT and
WHERE clauses!
Rails 5 added new validation on `belongs_to` to ensure the corresponding record exists. In the case of moving to the null list, this shouldn't trigger!
I wish we could flag that specifically `nil` is okay, but other values should be validated? But oh well, this is fine!
Ok so weird little situation, usually Arel will accept an attribute as a param to `order()`, but not when it's in a very specific situation of all of the following:
`Item.joins(:translations).includes(:translations).limit(30).order(Item::Translation.arel_table[:name])`
For some reason, it's all like "hey I can't call `to_sql` on an attribute!", but only in the scenario where all 3 of those other things are present. Weird!
Anyway, explicitly saying `.asc` fixes this. Ok!
Some important little upgrades but mostly straightforward!
Note that there's still a known issue where item searches crash, I was hoping that this was a bug in Rails 4.2 that would be fixed on upgading to 5, but nope, oh well!
Also uhh I just got a bit silly and didn't actually mean to go all the way to 5.2 in one go, I had meant to start at 5.0… but tbh the 5.1 and 5.2 changes seem small, and this seems to be working, so. Yeah ok let's roll!
In the interest of clearing out Resque, I'm just gonna remove a lot of our more complex caching stuff, and we can do a perf pass for things like big item list pages once everything's upgraded. (I'm hopeful that the upgrades themselves improve perf; and if not, that some improved sensibilities 10 years later can find simpler approaches.)
Ohh ok, without this change all of our `scope`s were just immediately evaluating the argument and fetching _all_ such matching records immediately, instead of waiting to actually be called. This led to bugs like `pet_type.as_json` returning ALL pet states in the whole db, because the `PetState.emotion_order` scope was being treated as a single predefined query, rather than a query fragment to merge into the current context.
This also explains what happened in 724ed83: that's why things before the scope in the query were being ignored.
We'll need to replace the item search query stuff with direct MySQL queries, but that's not ready yet bc the app still isn't booting, so we're committing this in a known broken state for now!
