Attachment dupes are a problem

[simonbaird]

Sometime the "purge_later" job fails. I don't know the reason for it, but the result is a stale leftover blob. This wouldn't be a problem, except that (it appears?) the stale blob is the one that is returned by the tiddlywiki_file assocation. This is a big problem because if the user reloads their site they get the old version, effectively losing the latest save.

Solution ideas:

• Figure out why the purge_later sometimes fails and fix it
• Include an "order by blob_id desc" somehow so the latest blob gets used. Some under the hood rails hacking would be needed. (Side note: This feels like a fix that could be useful in upstream rails.)
• Always purge immediately instead of later. (I looked into this and it's not actually possible in rails for some reason. An open issue from a while ago exists.)
• Instead of purge, do a detach, then have a background job for cleaning up old blobs. (Have to test this out, not sure if it's practical.)
• Switch the has_one_attachment to has_many_attachments, which would make it easy to select the newest. Then also have a background job to purge the old blobs. (This fits with the separate goal of keeping multiple versions, so there are some benefits.)
• A backgroung job to detect and quickly clean up stale blobs. (Feels like a band-aid solution hence probably a bad idea.)

[simonbaird]

I tried to reproduce the symptom locally by disabling the purge later job, and I wasn't able to. So I think there's something else going on. What happens is (somehow) the old ActiveStorage::Attachment record is still associated with the site, even though it should be not possible for a has_one_attachment association.

This makes me think maybe there's an error message produced when it happens.

[simonbaird]

For the order by workaround, I think this might do it:

+ActiveStorage::Attachment.class_eval do
+  default_scope { order('created_at DESC') }
+end

But I haven't been able to confirm it yet.

(It's not the blob that needs it, as I suggested originally, it's the attachment.)

[simonbaird]

A dupe appeared, and afaict the workaround is effective. I'll close this tentatively.